In the Japanese version, the cure promised by the aliens is specifically for all forms of cancer. However, in the American version the cure is for all diseases not just cancer.
In the US version, the original main title credits music (the "Monster Zero March") was replaced with a music track used later in the film (where the Planet X saucers collect the sleeping Godzilla and Rodan out of their habitats), allowing for a more eerie, foreboding theme.
There are some deleted scenes as listed below. A large prop foot of Godzilla was built for close up scenes of him stomping and kicking in houses and huts. In the final print of the movie there are a couple of quick scenes of this but originally there were approx. 6 different scenes of Godzilla's foot kicking in houses and huts that for some reason were cut from the finished film. A shot of Rodan on a hilltop blowing away tanks with his wings was cut for reasons unknown.
In the US version, the brief scenes of the Controller of Planet X speaking in the native Xian language were cut, as the US distributors deemed them to be too esoteric.
The American version of the film changes Tetsuo's name from Tetsuo Torii to Tetsui Terry.
In the American version, Godzilla's victory dance on Planet X included stomping sound effects whenever he landed. In the Japanese version, there are no sound affects except for his roars.