In this study, we fabricated flexible organic thin-film transistors on stainless steel substrates, and their electrical characteristic were measured under different bending conditions. We found that the electrical characteristic was increased under compressed strain and decreased under tensile strain. From the analysis of the results, we deduced that the variety of intermolecular force change the device characteristic under bending strain states. mechanical strains influence the barrier height between the grains of pentacene thin-films, thereby resulting in the variation of device characteristic.