The network's announcement Monday came one month after The Big C became the network's most-watched series premiere in more than eight years with 1.58 million viewers. That same night, the Season 6 premiere of Weeds drew 1.26 million viewers.
Both series will return sometime in 2011.
"The unprecedented viewership for both The Big C and Weeds proves that audiences love these shows as much as we do," Showtime President of Entertainment David Nevins said. "There are definitely more comedic adventures in store for these fascinating, complex women."
Weeds and The Big C air back to back Mondays starting at 10/9c on Showtime.