List of unmade monster films

Toho Company Ltd.

 * The Monster from 20,000 Miles Beneath the Earth (1953, became Godzilla)
 * The Volcano Monsters (1957, failed US revision of Godzilla Raids Again)
 * Continuation: King Kong vs. Godzilla (1963, direct sequel to King Kong vs. Godzilla)
 * Frankenstein vs. The Human Vapor (1963)
 * Godzilla vs. Frankenstein (1964, became Frankenstein vs. Baragon)
 * Operation Robinson Crusoe: King Kong vs. Ebirah (1966, became Ebirah, Horror of the Deep)
 * Batman vs. Godzilla (1966)
 * All Monsters Attack Directive (1968, became Destroy All Monsters)
 * Godzilla vs. The Mutant Starfish (1972, better known as Godzilla vs. Hitodah)
 * Godzilla vs. Hedorah 2 (1972)
 * Godzilla vs. Redmoon (1972)
 * Godzilla vs. The Space Monsters: Earth Defense Directive (1972)
 * The Return of King Ghidorah (1972)
 * Jet Jaguar vs. Megalon (1972/1973)
 * Godzilla vs. The Megalon Brothers: The Undersea Kingdom's Annihilation Strategy (1973)
 * Giant Monsters Converge on Okinawa! Showdown At Zampamisaki (1974, also known as Mechanical Monster Garugan)
 * Terror of MechaGodzilla (1975, early script draft / original version)
 * Nessie (1978)
 * U.S.-Japan Collaboration: Godzilla (1978)
 * King of the Monsters: Rebirth of Godzilla (1978)
 * A Space Godzilla (1978-1979, separate concept from 1994's Godzilla vs. SpaceGodzilla)
 * Godzilla vs. The Asuka Fortress (1979)
 * The Reawakening of Godzilla (1980, became The Return of Godzilla)
 * Godzilla: King of The Monsters 3D (1983, American production)
 * Godzilla 2: Godzilla vs. Biollante (1985-1989, original version of Godzilla vs. Biollante)
 * Godzilla 2: Godzilla vs. The Robot Army (1985-1989, became Gunhed)
 * Mothra vs. Bagan (1990)
 * Godzilla vs. King Kong (1990)
 * Godzilla vs. Mechani-Kong (1990)
 * The Return of King Ghidorah (1992, direct sequel / continuation of 1991's Godzilla vs. King Ghidorah)
 * Godzilla vs. Gigamoth (1992, became Godzilla vs. Mothra)
 * Godzilla vs. Mothra Sequel (1993)
 * Godzilla vs. Mechagodzilla II (1993, early draft versions)
 * Godzilla (1994, American production)
 * Godzilla vs. Bagan (1995)
 * Godzilla vs. Ghost Godzilla (1995)
 * Godzilla vs. Barubaroi (1995)
 * Yamato Takeru II (1997)
 * Godzilla 2 (1998-2000, attended sequel to Godzilla)
 * Godzilla Reborn (2001)
 * Godzilla vs. Kamacuras (2001)
 * Godzilla vs. M (2001)
 * Godzilla X Varan, Baragon and Anguirus: Giant Monsters All-Out Attack (2001)
 * Godzilla vs. Deathla (2003-2005, became Godzilla 3D To The Max)
 * Godzilla 3D to the MAX (2007-2009)
 * Godzilla (2012), became Godzilla (2014 film))

Daiei Motion Picture Company / Kadokawa Pictures

 * Giant Horde Beast Nezura (1965)
 * Gamera The Giant Monster vs. The Ice Men From Outer Space (1966)
 * Gamera vs. Two-Headed Monster W (1972, better known as Gamera vs. Wyvern)
 * Gamera vs. Garasharp (1972)
 * Godzilla vs. Gamera (2002)
 * Daimajin (2006, Takashi Miike)

Tsuburaya Productions

 * Ultraman: Operation Giant (1967)
 * Ultraman: Hero from the Stars (1978)
 * Ultraman: The Jupiter Effect (1978)
 * Yellow Eyes (2004, became Ultraman: The Next)
 * Ultraman 2: Requiem (2005)
 * Ultraman Mebius and the Ultra Brothers 2 (2007-2008)

Unproduced Television Projects

 * Unbalance (1965, became Ultra Q)
 * WoO (1966, later inspired 2006's Bio Planet WoO)
 * Scientific Special Search Party: Bemlar (1966)
 * Redman (1966, became Ultraman)
 * Ultra Eye (1967, became Ultra Seven)
 * Ultra Garrison (1967, became Ultra Seven)
 * Gridman Sigma (1994)
 * Ultraman Cross (2004, became Ultraman Nexus)

Toei Company Ltd.

 * Devil-Manta (1978)
 * Kongorilla (1977-1978)
 * Mortal (1980)
 * Rebellions (2011)

Willis O'Brien Projects

 * Creation (1930's)
 * The War Eagles
 * Gwangi (became The Valley of Gwangi)
 * King Kong vs. Frankenstein
 * Umbah
 * Last of the Labyrinthodons
 * Emilio and Guloso
 * Valley of the Mist
 * The Last of the Oso Si-Papu
 * The Bubbles
 * The Vines of Ceres

King Kong and Related Projects

 * The Eighth Wonder (1952)
 * Space Kong (1969)
 * King Kong In Africa (1976-1978)
 * King Kong In Moscow (1980's)
 * The Illegitimate Son of King Kong (1983)
 * Son of Kong (1986)

Ray Harryhausen Projects

 * The Jupiter Beast (1937-1949)
 * Food of the Gods (1949)
 * The Satyr (1946-1950's)
 * The Elementals (1952-1953)
 * Food of the Gods (1961, second attempt)
 * People of the Mist (1983)
 * Force of the Trojans (1984)

Other Unmade Giant Monster Films

 * The Big Freeze (1940's)
 * The Las Vegas Monster (1957)
 * Behemoth, the Sea Monster (1957, original version of The Giant Behemoth)
 * Attack of the 50ft Woman 2 (1958-1959)
 * Kuru Island (1961, became Gorgo)
 * Breakout of the Loch Ness Monster (1963)
 * Arkitius the Giant Squid (1966)
 * Monster Gigant (1966)
 * Monster Momonra (1966)
 * Reigon: Devil of the Seabed (1966)
 * G.O.O. - Genetic Octopodular Ooze (1971)
 * The Birth of Monster Nesugon (1973-1978)
 * Baby Kong (1976, Mario Bava)
 * Snails (1979)
 * It Ate Cleveland (1985-1987, better known as Godzilla vs. Cleveland)
 * The Dirty Filthy Slime (1988)
 * Tor (1991)
 * Gappa (1995, often mistaken for the otherwise false Gappa vs. Guilala)
 * Reptilicus 2 (2001)
 * Rampage (2011, based on the 1986 arcade game)
 * Notzilla: The Duke of Monsters (2011, though a promotional trailer was made)
 * Monster Roll (2012, though a promotional short was filmed)

Miscellaneous Projects

 * Stop! (television series, 1960's)
 * Godzilla vs. Terminator (Dark Horse Comics, 1990's)