Revealing mistake: Right as the Titanic hits the iceberg it does an underwater shot of half the ship. If you look closely, it really is only that half of the ship. The 3/4 size model they built was only half a ship, and they clearly didn't frame the shot right.
Continuity mistake: When Jack is howling at the front of the ship, he puts his arms up. His left arm is behind the rope, but in the next shot of him, his arm is in front of it. In the next shot, it is behind again.
Factual error: The car which brings Rose and Cal to the docks at Southampton has an RB registration plate. But RB wasn't introduced as a car registration index mark until 1929.
Audio problem: When the Captain is watching the overturned boat trying to be launched, there is a crew member working on the davit, causing it to make a rapid clicking noise. But soon after the noise stops, the crewmember is still turning.
Continuity mistake: After Rose has been persuaded to step into the lifeboat the camera is on Cal and Jack for quite some time when Cal reveals to Jack that there is no arrangement in his benefit. During all this time the lifeboat is being lowered, but when the camera cuts back to Rose she can still make eye contact with Jack almost at level.
Continuity mistake: When Rose and Jack run outside after making love in the car, you will notice a shot of the men in the lookout tower where you can see their breath due to the extremely cold night. But when the shot goes to Jack and Rose, you will notice that you cannot see their breath but also Rose does not seem to be affected by the cold even though she is wearing a thin dress with no sleeves.
Factual error: In the shots taken in the grand staircase, the lights on the ceiling are flush with the ceiling itself. The lights in the actual Titanic's grand staircase were mounted via a small pedestal. Earlier in the film when the submarine is exploring the grand staircase, there is a shot of one of these same lights except this light actually has the original pedestal.
Factual error: Margaret Brown never went by the name of "Molly" Brown during her lifetime. It was not until after her death that she was referred to as "The unsinkable MOLLY Brown".
Factual error: Those USA $20 bills that Caledon Hockley stuffs into the pocket of First Officer Murdoch are Federal Reserve Notes, which were first issued in 1914.
Continuity mistake: When Rose, Cal and the others sit around a table talking and drinking, and Mr Ismay says something. His hands are locked together by his fingers, but in the following wide shot his left hand is down by his knee and his right is holding a fork with food on it. Also, Rose puts the cigarette holder to her mouth and takes her left hand away from it but in the following shot her left hand is still on it.
Continuity mistake: Right after the 1st smokestack has fallen and crushed Fabrizio, it is seen from above creating huge sprays of water. The problem is that the smokestack looks nothing like the Titanic's. You can see the top and there is no black whatsoever. And to make it stranger, there is a cable attached to it and then one below it, both on the peach/orange color, and not the black.