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)