An amorphous carbon (a-C) film is deposited on the plasma-treated UHMWPE substrate using a closed field unbalanced magnetron sputtering to improve its tribological properties. During the plasma treatment period, a transition layer is prepared by high energy ion bombardment at a bias voltage of -500 V to enhance the adhesion between the a-C film and the substrate. The mechanical and tribological properties of the a-C film were evaluated by nano-indentation and ballondisk tribometer. After deposition of a-C film with a thickness 900 nm, the nanohardness of UHMWPE significantly increases from 47 MPa to 720 MPa and the wear rate decreases from 9.82 x 10(-15) m(3) N-1 m 1 to 4.78 x 10(-15) m(3) N-1 m(-1) in bovine calf serum solution. The formation of the transition layer is believed to be the reason why the vertical adhesion between the a-C film and the UHMWPE substrate is enhanced. (C) 2015 Elsevier B.V. All rights reserved.