The rear cross member structure includes a cam bolt seating unit formed in a rear cross member and having a cam bolt which fixes a lower arm and is seated in the cam bolt seating unit, a cam bolt insertion hole unit formed in the cam bolt seating unit and having the cam bolt inserted into the cam bolt insertion hole unit, and a cam bolt guide unit protruding from the cam bolt seating unit and configured to guide a rotation of the cam bolt by being brought into contact with sides of the cam bolt.