The show will air May 11 on CBS, the New York Post said Wednesday.
The last time an original episode of the series aired was in 1966.
Now Reiner, who created the show, has written a new episode starring the original cast, minus Morey Amsterdam, who played comedy writer Buddy Sorrell and died in 1996.
Set in the present-day, the episode finds Rob Petrie, who's still married to Laura, getting a phone call from his former boss, prickly Alan Brady.
Brady wants Rob and his comedy-writing partner, Sally, to write his eulogy--figuring that way he will know what people will say about him when he dies.
"Everybody Loves Raymond" star Ray Romano will host the episode, which will also include clips from the original series.