The Kourtney & Kim Take New York star confirmed that she is expecting again in a cover interview with the new issue of Us Weekly, which hits newsstands on Friday.
Kardashian added to E! News: "Scott and I are so excited to announce that we are expecting our second child and are thrilled to be expanding the love in our family."
Disick told Us that the couple hadn't been actively trying for a second child, but added: "It wasn't like we weren't trying. We kind of just said, 'If it's meant to be, it'll be'."
The couple are already parents to son Mason.
Kardashian and Disick can be seen in the new season of Kourtney & Kim Take New York, which returned to E! for its second season last week, attracting 3.2 million viewers.
Kardashian's pregnancy announcement comes the same week that she launched a 'Mommy Blog' on her official website to share hints and tips on motherhood with her fans.
Her first video blog focused on children's fashion as she took viewers on a tour of Mason's closet.
Kourtney & Kim Take New York continues Sundays at 10pm on E!