A chain tensioner includes a housing having a closed bottom. A rod is axially movably inserted in the housing for pressing a chain. A wear ring is mounted to the outer periphery of the rod and is biased by a return spring mounted in the housing in a direction away from the bottom of the housing. A nut member is mounted between the wear ring and the bottom of the housing so as to be coaxial with the housing and axially movable relative to the housing. A ring-shaped spring member is provided between the nut member and the bottom of the housing to support the nut member. A screw rod is provided between the rod and the bottom of the housing and in threaded engagement with the nut member. A spring is provided between the screw rod and the bottom of the housing to bias the screw rod in a direction away from the bottom of the housing. The screw rod has an end surface that is in abutment with the rod.