The reality TV starlet cited irreconcilable differences in court papers filed Monday morning in Los Angeles Superior Court. The papers also state that there was a prenuptial agreement, but gave no further details.
Kardashian, 31, and Humphries, 26, wed before some 500 guests on Aug. 20 at a $20-million estate in Montecito, Calif., near Santa Barbara.
The NBA player said he was blindsided by the news that his wife wants out, saying, "I love my wife and am devastated to learn she filed for divorce."
But the Kardashian family is standing by her decision.
"It's a very tough time obviously for our entire family, and especially for my sister Kim, but we're always there as a family, supportive always no matter what decision she makes," Rob Kardashian said Monday night after his "Dancing With The Stars" performance. "It's just our job now to be there for her."
Kim Kardashian, who is in Australia on business, addressed the divorce only through a written statement.
"After careful consideration, I have decided to end my marriage," she said. "I hope everyone understands this was not an easy decision. We remain friends and wish each other the best."
The divorce will be Kardashian's second. She married her first husband, music producer Damon Thomas, in 2000, when she was 19 years old. The two divorced in 2004.
Kardashian stars on the E! reality show "Keeping Up With The Kardashians," along with sisters Kourtney and Khloe. Humphries last played as a forward for the New Jersey Nets.