Substrate surface roughness predominantly influenced grain size of pentacene in vacuum-deposited thin films while surface energy of the substrate did not, i.e., larger pentacene grain was obtained on a Substrate with lower roughness instead of lower surface energy. On the other hand, grain size of C-60 deposited in the same manner was influenced by both surface energy and roughness, i.e., large C-60 grain was obtained on substrates with lower surface roughness and energy.