In South Korea, a family gathers for the wedding of an astronaut, however, the astronaut is called back to duty to monitor a nuclear test in the Middle East. The test triggers an earthquake that shifts the epicenter to the heart of Korea. The authorities initially withhold this information from the public until they’re sure the quake strikes but once the earthquake reaches the Hwanghae province, the authorities impose martial law for the area.
The quake strikes Panmunjom, where a photographer takes pictures of the ground splitting, which reveals a giant creature moving inside. The photographer manages to get away but crashes his car due to the quake. The photographer manages to reach the authorities and deliver the photographs of the creature before succumbing to his injuries. The authorities name the creature “Yongary”, after an old Korean fable about a monster connected with earthquakes.
While South Korea is being evacuated, the military is dispatched to the Inwang area to attack Yongary but with no success. Il-Woo, a young scientist, decides to go to Seoul to find a weakness in Yongary. His girlfriend, Soona, opposes this but he goes anyway. Soona and her younger brother, Icho, pursue Il-Woo to try to stop him. Yongary eventually reaches Seoul and causes complete destruction. During the rampage, Il-Woo and Soona lose Icho and walk around trying to find him.
The military suggests using guided missiles against Yongary but the authorities fear the missiles might do more damage than the monster and may destroy the landmarks of old Korea, however, the authorities decide that Korea’s future is more important and agree to use the guided missiles. Icho manages to escape through the city’s sewers and reaches an oil refinery where he finds Yongary drinking oil and gasoline. Icho turns off the main valve which causes Yongary to go berserk and destroy a tank that triggers a chemical reaction that makes Yongary itch and scratch.
Icho then returns to Il-Woo's house to tell him what happened at the refinery. Il-Woo then reveals this discovery to the authorities and urges them to not use the guided missiles because they will give him more energy but his claims are brushed off and they proceed with the missile plan regardless. Il-Woo then goes to work on a chemical to defeat Yongary using a precipitate of ammonia.
Yongary is then struck with Il-Woo's ammonia and missiles, which is enough to put him temporarily to sleep, however, Il-Woo believes the ammonia needs more work. Icho takes a light device from Il-Woo's lab and shines it on an immobile Yongary, which triggers him to wake up. To Icho’s amusement, Yongary then begins dancing but then returns to his rampage.
Il-Woo loads the finalized ammonia onto a helicopter and dumps it on Yongary in the Han River, where Yongary collapses and dies. The following morning, Il-Woo is commended for his role in defeating Yongary, however, he cites Icho as the real hero for providing him with the information of Yongary’s eating habits. In the end, Icho opines that Yongary was not evil by nature but rather, simply looking for food.
- Oh Yeong-il
- Kwang Ho Lee
- Nam Jeong-im
- Lee Sun-jae
- Moon Kang
- The monster suit was designed in South Korea, but built by a Japanese team in Japan.
- The original South Korean cut of the film, Great Monster Yongary, is partially lost, with only forty-eight minutes of the original footage remaining.
- In 1999, Yongary was remade as "Yonggary". The remake was released in the United States as Reptilian in 2001, with cover art that made an attempt to capitalize on the 1998 release of the American Godzilla. Both versions feature the same CGI effects. .