Newsom said Monday that the 69-year-old inmate shouldn't be released. She's spent nearly half a century in prison and received reports of good behavior and testimonials about her rehabilitation.
Van Houten was 19 when she and other followers in Manson's cult fatally stabbed wealthy Los Angeles grocer Leno LaBianca and his wife, Rosemary, in August 1969.
The killings came the day after other Manson followers killed pregnant actress Sharon Tate and four others. No one who took part in the Tate-LaBianca murders has been released from prison.
Governors have rejected parole three times for Van Houten.
It's the first time Newsom denied her freedom. Former Gov. Jerry Brown rejected her release twice.