We have investigated the decomposition of C-60 molecules with low and high coverages on Si(100)(2 x 1) surface at elevated temperatures. We also investigated the decomposition of an isolated C-60 molecule. We employed molecular-dynamics simulation using a model potential. It has been found that C-60 decomposes on Si(100) surface after 1000 K in the case of low coverage (0.11), however in high coverage case (0.67), C-60 molecules decompose after 900 It. On the other hand, isolated C-60 molecule decomposes after 7500 K, interestingly it shows a phase change from 3D to 2D at higher temperatures.