We have examined the effect of annealing on physicochemical properties of the diamond-like carbon (DLC) films to produce higher quality films by the electron spin resonance spectral analyses of the immobilized dangling-bond sites (DBS), since amount of DBS reflects the characteristics of DLC films. On heat treatment of DLC deposited from ethylene monomer under anaerobic condition, the DBS decay was clearly shown, as the temperature raised. The decay described by second-order kinetics indicated that the recombination reaction of DBS progressed on heat treatment, suggesting that annealing treatment would accelerate the carbon-carbon covalent bonding network to produce harder films. In fact, the resulted DLC film derived from ethylene monomer showed non-existence of any type of oxygen atom based on X-ray photoelectron spectrum measurement, and water contact angle measurement showed higher hydrophobic surface of the DLC films. (C) 2011 Elsevier B.V. All rights reserved.