The star replaced Charlie Sheen in the hit CBS sitcom this season, which saw viewing figures fall to 14.85 million, according to The Nielsen Company figures, The New York Daily News reported.
Kutcher tweeted this week: "It took us a couple weeks but I think Two And A Half Men has found the groove. Thank you for supporting the show again last night!"
The show, co-starring Jon Cryer, is still the most-watched sitcom on television, and Kutcher's debut episode on September 19 was seen by 28.7 million people, more than any other episode in the show's first eight seasons, when Sheen was the star.
The show is still above last year's average total of 12.7 million viewers per episode.
Last year it averaged 4 per cent of 18 to 49-year-olds, the audience favoured by advertisers, while Monday night's episode held 5.2 per cent of that audience.
Sheen was fired from the show last season for drug use and erratic behaviour.
Record viewing figures tuned in to see how his character - Charlie Harper - would be replaced by Ashton.
Charlie Harper was killed when he was hit by a subway train in Paris and Ashton appeared as an internet billionaire, who survived an unsuccessful suicide attempt over a crumbled relationship.