Two unidentified sources in China told the South Korean news agency that Kim Yo Jong married Choe Song, the son of a senior adviser.
"As far as I know, Kim Yo Jong, deputy director of the Workers' Party, got married to a son of the party's secretary Choe Ryong Hae," one of the sources said.
The elder Choe made headlines in November when he traveled to Moscow as a delegate of the Supreme Leader to boost Pyongyang's relations with Russia amid cooling ties with China.
The marriage could signify an attempt by the Kim family to further strengthen its control over influential officials.
Estimated to be 28 years old, Kim Yo Jong is the youngest sibling of the Supreme Leader and appears to have risen in the ranks following the death of her father, Kim Jong Il, in 2011. There was speculation in November that she was temporarily in charge while her brother was recuperating from ankle injury.
She appeared in a photo Friday wearing what appeared to be a wedding ring on her left finger.