Diamond-like carbon (DLC) films were deposited on ultra-high molecular weight polyethylene (UHMWPE) and polymethylmethacrylate (PMMA) with oxygen plasma pre-treatment using a radiofrequency plasma chemical vapour deposition method. A ball-on-disc test was carried out to evaluate the wear properties of the DLC-coated UHMWPE and PMMA. After testing, the surface of the polymers was observed using an atomic force microscope and an optical microscope. The adhesive strength of the DLC films deposited on the polymers was measured using a scratch test. After the ball-on-disc test, many cracks were observed in the films on the surface of both the DLC-coated UHMWPE and PMMA without the oxygen plasma pre-treatment, whereas the DLC-coated UHMWPE and PMMA with oxygen plasma pre-treatment showed no cracks and good wear resistance. In the scratch test, the adhesion strength of the DLC film to the PMMA substrate increased from 42.5 mN to 101.3 mN with oxygen plasma pre-treatment.