Smith, 80, said the next season will be her last, irrespective of the speculation of whether the sixth season will be the final season of the show, said The Hollywood Reporter.
"They say this is the last one, and I can't see how it could go on. I mean, I certainly can't keep going... To my knowledge, I must be 110 by now. We're into the late 1920s," she said.
Smith's witty and cutting Dowager Countess has been one of the series' most popular and memorable characters and has won her critical acclaim too with two Emmys and a Golden Globe.