Continuity mistake: When R2D2 is captured by the Jawas, a Jawa welds a restraining bolt to the middle of a panel on R2. When the shot changes to a close up, it's being attached to the top of the panel. The shot changes again, and it's welded to the middle again.
Other mistake: When Han Solo, Luke, Obi Wan, C3PO and R2-D2 are on their way to the Millennium Falcon for the first time there is a scene where they have to walk down a few stairs. If you look carefully you can see that R2-D2 is struggling to get down the stairs but in the next shot he's down with the others.
Continuity mistake: Widescreen version: In the trash compactor, Han says to Leia, "Get on top of it." In the next shot, Leia can be seen in the background, in a totally different position from the previous shot. For example, she is holding the pole differently. (01:20:25)
Continuity mistake: When in the Death Star, there is a shot of five stormtroopers standing next to the Millennium Falcon. Two of the stormtroopers are right next to the boarding ramp. The camera instantly changes to a higher point of view and the two stormtroopers have moved about four feet farther away from their original spots.
Continuity mistake: When Luke sees the holograph of Princess Leia for the first time, and says, "Who is she, she's beautiful," Mark Hamill's hair is rather tousled. In the next shot of him, it's neatly combed. Then, when he gets up and says, "Well I don't know anyone named Obi-Wan...," his hair is tousled again!
Continuity mistake: When Luke has been knocked unconscious by the Sand People and Obi-Wan appears and scares them off, there's a shot of Luke lying there and one of his sleeves is in disarray, halfway up his arm. But when Obi-Wan checks his pulse, he does it right through a fully-covered-by-the-sleeve wrist. (00:28:25)
Revealing mistake: Special Edition: When Luke and Obi-Wan are arriving in Mos Eisley to find a pilot, the Ronto in the background throws the Jawa riding him to the floor. When the Jawa falls to the ground a puff of dust is seen and a thud is heard, but look closely - he never actually hits the ground.
Continuity mistake: When Luke first sees the holomessage from Leia, she is bending down to stop the recording while still saying "Help me Obi Wan Kenobi, you're my only hope." When the message is viewed for the second time, she finishes speaking, looks around, and then bends down to stop the recording.
Revealing mistake: Original version: When the Gold Leader says to the Red Leader "Red Leader, this is Gold Leader" at the start of the Battle of Yavin, the two Y-Wing fighters outside his cockpit suddenly disappear. (01:46:05)
Continuity mistake: After the Stormtroopers have captured Leia aboard the Blockade Runner and are leading her to Vader, one Stormtrooper's armour is visibly damaged (http://s253.photobucket.com/albums/hh67/RoofingGuy/BrokenStormy.jpg). For the close-up of Leia, the damage has been masked with white gaffer tape (http://s253.photobucket.com/albums/hh67/RoofingGuy/FixedStormy.jpg). [Timecode from 2008 Widescreen DVD release. similar time on the "Theatrical Release" bonus disc.]. (00:07:25)
Continuity mistake: During the fight against the TIE fighters, the interior shot shows the turrets on the Falcon both point straight up and down respectfully, when in other shots the top turret for example is facing forward.
Deliberate mistake: During the 4 Tie Fighter attack you can see the blue screen octagon matte leftovers surrounding the Tie's trying to blend into space. However it's not the same type of black, so they glow a bit. They are constantly confused as shields, but they aren't. It's real easy to spot if the contrast and lighting on your TV is a bit high, but I spotted it without that.