Continuity mistake: When the spaceship first springs a leak and begins to sink, the interior shots show it tilting to starboard; Taylor falls against the starboard bulkhead and the other two survivors need to brace themselves from slipping. All of the exterior shots of the ship show it level from port to starboard.
Continuity mistake: The first exterior shots of the spacecraft in the desert lake show the spaceship's hatch door already gone... before the astronauts blow it off with an explosive charge minutes later in the movie.
Revealing mistake: Toward the end of the film, in a long-shot, an ape hits another in the head with the butt of his rifle, knocking him over. You don't even have to look closely to see that the rifle's butt never even comes close to making contact with him.
Continuity mistake: When Taylor, Landon and Dodge discover the humans, when Dodge says "Blessed are the vegetarians", both Taylor and Dodge are standing even with each other and Landon is standing about an inch or two behind Taylor and Dodge. In the next shot, Landon and Dodge are standing even with each other and Taylor is standing almost a foot away from Landon and Dodge.
Continuity mistake: When Taylor is trying to describe where he came from to Zira and Cornelius, he has Cornelius hold up a map. Cornelius holds the left side and Taylor holds up the right. As Zira says "You fell into the water here?", the map is slanted to the side. In the next shot, Taylor suddenly isn't holding the right side of the map and the map is more levelled out.
Continuity mistake: After the ship has sunk, Taylor, Landon and Dodge make camp on some rocks. In the shot where Taylor says "Dodge, run your soil test. Got your sensors? Geiger counter?" in the background is the life raft used when they escaped the ship. The raft is resting on some rocks that are bright colored. In the next shot, in a shot of Landon the rocks the lift raft is resting on are all dark colored. The raft has also moved closer to the water.
Visible crew/equipment: When the astronauts are running down a dusty hill in the desert, you can spot the shadow of the camera on the back of Landon and Dodge.
Plot hole: Wouldn't Taylor have suspected he was still on Earth, seeing as all the apes were speaking English?
Revealing mistake: Towards the end of the movie, at the cave, you can see that the rifle Charlton Heston has been firing has no magazine inserted.
Continuity mistake: Shortly after the astronauts crash land in the desert lake, they discover that the female crew mate is dead, her body is mummified due to an air leak in her cubicle. The mistake is that when her body is first seen, the arms and hands are folded across her chest. Seconds later, when the water starts rushing in, the point of view from inside her cubicle shows her arms at her sides.