We have demonstrated that the photoalignment method could be used to control the structural anisotropy of pentacene films, an active semiconducting layer, in thin-film transistors (TFTs) with conspicuously anisotropic electrical characteristics. The photoaligned pentacene films were characterized with respect to structure and morphology using X-ray diffraction and atomic force microscopy. Compared to the pentacene films that are not controlled, a maximal 25-times increase in field-effect mobility (up to 0.75 cm V-1 s(-1)) has been achieved in the photoaligned pentacene-based TFTs by aligning pentacene orientation parallel to the direction of current flow with the help of a photoaligned polyimide layer. Mobility anisotropic ratio in the range of 2.7-8.3 for the current flow parallel and perpendicular to the alignment of the photoaligned pentacene films have been observed for photoaligned pentacene-based TFTs.