A solid solid crystalline transition from beta to alpha forms in syndiotactic polystyrene (sPS) was found during the mechanical deformation in the temperature range of 130-218 degrees C, studied by X-ray and infrared spectroscopy. alpha and beta forms, in contrast to the other two crystalline structures (gamma and delta forms) in sPS, are two major crystalline forms manufactured through a concise molding process which is industrially readily accessible. There have been a number of structural transitions found between two crystalline structures among the four different crystalline forms of sPS. In this work, beta to alpha form transition at well below the melting temperature of sPS (similar to 270 degrees C) was found by mechanical deformation, which became more pronounced as temperature increased. The structural transition was intimately related to the crystallization temperature and the densities of alpha and beta forms.