Laser-induced structural decompositions of hydrogenated amorphous carbon films deposited by dc-magnetron sputtering on magnetic hard disks were studied using a microbeam Ar + laser (514.5 nm). The laser had varying powers between 3.0 and 0.3 mW at a focused circular spot of 2.5 μm diameter, corresponding to approximate fluence rates between 6×10 4 to 6×10 3Jcm -2s -1. The effect of laser power on decomposition rate could be expressed by an exponential equation. Based on the relationship between laser power and temperature, relative apparent activation energies for film decompositions were obtained and found to decrease with the increase of film hydrogen content and the elapse time of laser irradiation. All the films irradiated with laser powers between 0.75 and 0.3 mW followed the apparent first-order reaction. The reaction order tended to increase at higher laser powers and hydrogen content in the films.