Continuity mistake: In the Emperor's throne room, the existence and arrangement of several of the canisters on each side of the lift/elevator changes between shots, several times.
Continuity mistake: During the battle against the Death Star, right before the Emperor gives permission to fire the Death Star, Wedge says, "Red Three, Red Two, pull in." Another pilot answers, "Got it", but it is neither Red Two nor Three, but Green Leader. (01:36:25)
Revealing mistake: If you watch closely (or play it in slow motion) when the scout trooper punches Han, you can see that the troopers hand never actually comes into contact with is face. (00:55:45)
Continuity mistake: When Chewbacca gives Han a hug in his prison cell in Jabba's palace, he initially puts one arm around him, but as the shot changes both Chewbacca's arms are around Han.
Continuity mistake: In the fight scenes on the skiffs with Jabba the Hutt's men, the skiff that Han and Chewie are on is hit with a laser blast and Han falls over the edge feet first, yet in the following scene he is hanging upside down with Chewie holding his feet.
Revealing mistake: In the shot where Vader throws the Emperor into the pit, the Emperor is obviously a puppet, because he doesn't move at all. (01:52:15)
Continuity mistake: When the Rancour grabs Luke, as the shot ends, Luke is holding the bone with two hands. In the next shot, he's holding it with only one hand. (00:25:20)
Continuity mistake: When R2-D2 is tied up in the Ewok village, the rope that binds him keeps changing position.
Continuity mistake: Just before the Emperor's ship lands on the Death Star, a formation of four TIE fighters disappears from the center right of the frame. This happens seconds before the in-hangar scene with Vader greeting the Emperor. This is visible on VHS.
Continuity mistake: After Lando is shot off the transport vehicle when Han is trying to save him, look for Lando to actually walk down the sand in the bottom of the screen. The very next scene, he is hanging on the rope.