The Associated Press said "there were no immediate details on the role Aniston will play - as herself or a fictitious character - or the episode's planned air date."
The New York-based series, which begins its third season in October, stars Tina Fey and Alec Baldwin in a behind-the-scenes, sometimes self-directed spoof of a television network and the huge corporation that owns it. The show has won a modest but devoted following, and critical raves. Awards include Golden Globes, a Peabody and last year's Emmy for outstanding comedy series.
30 Rock begins its third season in October, and stars Tina Fey and Alec Baldwin.