The network decided to drop both series due to poor ratings, Entertainment Weekly reports.
The network's executive vice president of programming, Stephan Shelanski, confirmed: "After careful consideration, we've decided not to continue on with subsequent seasons of Party Down and Gravity.
"We're grateful to everyone involved in the shows, and are proud to have had them on the channel. Starz remains committed to aggressively expanding our original programming lineup."
Starz aired just ten episodes of Gravity, which starred Ving Rhames. Party Down ran for two seasons on the channel, with star Adam Scott recently admitting that he was hopeful the show would be renewed.