In this study, we simulated moist-air flows through a 3-D transonic compressor rotor, NASA Rotor 37, to investigate the thermophysical effects of evaporation of water droplets on 3-D compressor aerodynamics. The obtained results indicated that the total pressure ratio increased in the moist-air cases when compared with dry-air case as a result of the cooling due to evaporation. While the choking mass-flow rate is almost identical for the dry-air case and the moist-air cases, the operating curve was shifted to nearly choked state in the moist-air cases. Besides this, unsteady flows were obtained at higher mass-flow rate in the moist-air cases when compared with the dry-air case. As a result, a significant deterioration in the operation was observed in the moist-air cases. This is due to the rapid and significant evaporation of water droplets after the passage shock. A secondary flow streaming radially outside toward the tip through the separated region intensified and contributed to a formation of large blockage around the tip region.