The endorsement in the latest of series of high-profile endorsements for Kashkari, a moderate Republican who trails tea party favorite Tim Donnelly badly in public opinion polls. Former California Gov. Pete Wilson, former Massachusetts Gov. Mitt Romney and former Florida Gov. Jeb Bush have all endorsed Kashkari.
Rice is beloved by California Republicans, many of whom have hoped for years that she would run for governor. Kashkari, a former U.S. Treasury Department official, has said he would not have entered the race if she were running.
Rice spoke at the California Republican Party convention outside San Francisco in March, urging delegates "to rebuild this party, to rebuild our nation, and to rebuild our world."
Rice, a professor at Stanford University, has repeatedly said she is not interested in running for elected office.
In the endorsement release from the campaign, she said Kashkari's "focus on uniting Californians around fiscally conservative economic principles is the right message to help us grow the Republican Party in California and across the nation."
PHOTO: Republican Neel Kashkari speaks with reporters at Oroville Dam on March 28, 2014. The Sacramento Bee/David Siders