Continuity mistake: When the Imperials are tricked into leaving the bunker, they are surrounded by Ewoks, and as the shot ends, if you look through the crowd, you can see that Han turns his head to his right. In the next shot, he's facing forward again.
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.
Continuity mistake: In the first shot of the Emperor's force striking Luke, the Emperor's hands are in a different position from the previous shot. This also happens after he says, "You have paid the price for your lack of vision."
Continuity mistake: In the beginning of the scene where Luke is being electrocuted by the Emperor, the Emperor is standing at the bottom of the stairs. When he says, "Young fool... Only now, at the end, do you understand", he is standing in front of the great window. However, in the next shot of the Emperor, he is standing at the bottom of the stairs again, before he walks down to his previous position.
Other mistake: Widescreen version: When Han calls after Luke and Leia when they leave on the speeder bike, the head of the stormtrooper that attacks him can be seen in the lower right hand corner, as the actor is waiting for his cue. After Han calls after Luke and Leia, the stormtrooper suddenly pops up and attacks him.
Revealing mistake: At the beginning of the ground battle on Endor, two stormtroopers are knocked to the ground by the Ewoks. In the following shot, one of the troopers has a big crack in the left shoulder of his armour. The crack was obviously not there in the previous shot.
Other mistake: After the catwalk that Luke is standing on collapses, Vader walks down the stairs to find him. In the first shot, there's a shadow of a lightsabre blade on the right side of the steps, but Vader's sabre is extinguished at this point. It can't be the shadow of Luke's sabre. Widescreen version only.
Deliberate mistake: The shots of the prisoner skiff during the transport to the Sarlacc Pit are reversed. This can, for example, be seen as Chewie's bandolier is on the wrong side, and that Han's shirt is overlaying the wrong way.
Revealing mistake: When Luke leaves the Death Star in an Imperial shuttle, a large girder or something falls right in front of his ship. If you watch closely, you can see it bounce, revealing the miniature. A huge, heavy girder wouldn't have bounced like this.
Continuity mistake: Before the Emperor gives permission to fire the Death Star, in the scene at the bridge of the Star Destroyer, the blue rank insignia of Admiral Piett and another Imperial officer is coloured black. This is probably caused by bluescreen effects replacing everything blue with the colour of space. This can also be seen when a Rebel ship hits the Star Destroyer at the end of the film.
Continuity mistake: In the first shot of the hologram of Endor and the Death Star, the Death Star orbits Endor in an counter-clockwise direction. In the subsequent shots, the Death Star orbits in a clockwise direction.
Continuity mistake: In the beginning of Luke and Vader's lightsabre duel, and also in a few shots right after Luke knocks Vader down the stairs, Vader's cape alternates between being draped behind and over his left shoulder.
Continuity mistake: In the first shot of Chewbacca when he is in Jabba's dungeon with Han, his bandoleer is on the wrong side.
Continuity mistake: On the forest moon of Endor, when the stormtrooper punches Han, he falls and has a blaster in his hand but it disappears when he hits the ground. He can't have thrown it during the time he was falling, because he shot accidentally when he was near the ground. If he has thrown it, it should have been near him.
Revealing mistake: In the scene where Han and Lando are talking in the hangar after the big meeting about the new Death Star, right when the scene opens and the shot pans down, notice how half the hangar is real and the other half is a matte painting.
Continuity mistake: In one scene of the battle of Endor, Chewbacca is accompanied by 2 Ewoks while pursuing one of the ATSTs. However soon after their first appearance, one of the Ewoks' costume looks completely different from the original one.
Continuity mistake: Just after R2-D2 cuts the net that holds him, Luke, Han, Chewbacca, & C-3PO, you can see that before the Ewoks pop up out of nowhere to see their captured victims, one Ewok just stands there in plain sight waiting for the others to reveal themselves.
Revealing mistake: Just before Luke chops off Darth Vader's hand in the battle at the end of the movie, you can see that the bar has already been cut (the line is visible) to give the illusion that Luke cut through the steel bar with his lightsaber as well as Vader's hand.