An organic-inorganic halide CH3NH3SnI3 perovskite with significantly improved structural stability is obtained via pressure-induced amorphization and recrystallization. In situ high-pressure resistance measurements reveal an increased electrical conductivity by 300% in the pressure-treated perovskite. Photocurrent measurements also reveal a substantial enhancement in visible-light responsiveness. The mechanism under lying the enhanced properties is shown to be associated with the pressure-induced structural modification.