Continuity mistake: As we follow Fett's flight after being hit by Han, we cut to a scene showing the front half of a skiff. Luke then kicks one of Jabba's henchman. He very clearly misses the man by a few inches, yet the man still tumbles to his doom nonetheless.
Continuity mistake: When Han, Luke and Chewbacca are sentenced to death, there's a strange alien with a long tongue hanging from the ceiling, in the upper, left hand corner. In some shots, the creature is moving, in other shots, it is completely still and appears to be asleep or something.
Continuity mistake: After Luke kills the Rancour, Jabba says, "Bring me Solo and the Wookiee", and Lando is nowhere to be seen. In the next shot, he is suddenly standing in front of Jabba's platform, and some of the other people have changed position. (00:27:00)
Other mistake: Look at the shots of the windows in the Emperor's chamber on the Death Star. When they are seen from a distance, the window frames are out of focus, but the stars remain in clear focus.
Continuity mistake: In the scene on Endor where Luke and the Stormtrooper are duelling on the speeder bikes. The glove on Luke's damaged hand changes sides between the front and side on shots.
Revealing mistake: In one quick scene when Luke's hologram is talking to Jabba, the film has been reversed. The camera shows Jabba sucking on his 'bong' and then pans down to Salacious Crumb. However, during the Jabba shot, the air bubbles in the 'bong' are going down, as opposed to surfacing. Behind Jabba, you can see the smoke created is also going downward.
Continuity mistake: At the very end of Palpatine and Vader's conversation, we are tight on the Emperor. He is walking past a series of grey suited officers. But when we instantly cut to a wide angle shot, they are now in front of rows of stormtroopers.
Continuity mistake: This is a 'Special Edition' error only. After the scene in Jabba's palace when R2D2 and C3P0 are assigned their 'duties' we see the audience chamber in their party, and Jabba holding his dancing girl's leash. When the first song ends, Jabba says 'Do that again' and his hands are empty. When next he's shown, the leash is back in his hands.
Continuity mistake: Widescreen version: When the captured rebels are led out of the bunker, C-3PO walks out from behind a tree. In the next shot, the tree is much bigger, and C-3PO is further away from it. (01:33:10)
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. (00:56:15)
Continuity mistake: When the droids enter Jabba's throne room, in the shot facing the droids, they are not standing on the same part of the floor as in the previous shot. Also, R2-D2 is facing Jabba, but in the previous shot, he was facing C-3PO. (00:08:15)
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 the droids enter Jabba's throne room, a three-legged R2-D2 rolls out on the floor. In the next shot, the droid no longer has his third leg deployed.
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)