The show premiered on celebrity network E! in July last year, three months after Jenner's first TV interview about transitioning from a man to a woman and giving up Bruce, the name she was known by as the 1976 Olympics decathlon champion.
"After 2 amazing seasons of @IAmCait, it's time for the next adventure," Jenner tweeted.
"Thank you E! & thank you to the best girlfriends I could ask for!"
The eight-episode first season managed an average of just 1.4 million weekly viewers, while the second season, which began in March, dipped below a million.
E! said in a statement it was "incredibly proud" of a "groundbreaking docuseries that sparked an important and unprecedented global conversation about transgender people," adding that the cancellation was a mutual decision between Jenner and the network.
The 66-year-old, an avowed Republican and perhaps the world's most famous transgender woman, became an icon of the LGBT (lesbian, gay, bisexual and transgender) movement when she announced her gender transition.
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