Smith, 78, has won numerous awards for her portrayal of acid-tongued Violet Crawley, the Dowager Countess of Grantham, on the show, which airs in the United States on PBS each season after its ITV premiere.
Asked in a "60 Minutes" interview to air Sunday if she is proud of the show, Smith hesitated, EW.com reported.
"I haven't actually seen it, so I don't -- I don't sit down and watch it," she said.
"Never?" her interviewer pressed.
"No, I haven't watched it," she said.
Smith went on to explain she is a perfectionist who doesn't want to see what she might have done differently by reviewing a finished film or TV show.