A child safety seat includes a seat body, a support foot and an angle adjusting mechanism. Two support ribs are disposed at opposite sides of a bottom of the seat body. Each of the support ribs includes a front support end and a rear support end. The support foot is disposed between the two support ribs and pivotally connected to the two support ribs. The angle adjusting mechanism selectively adjusts and fixes the support ribs and the seat body such that one of the front support end and the rear support end supports the seat body on the vehicle seat along with the support foot. Accordingly, the child safety seat of the invention is capable of adjusting an angle of the seat body and supporting the seat body securely.