The objective of this study is to clarify the Mach number effect on the aerodynamic characteristics of airfoils at low Reynolds number. In this study, we conducted airfoil tests using a flat plate and a triangular airfoil in the Mars Wind Tunnel at Tohoku University. Reynolds number was set at 3,000 and 10,000 and Mach number at 0.15, 0.5 and 0.7. Aerodynamic force and pressure distributions on the models were measured using a force balance and Pressure-Sensitive Paint (PSP). The results show that the compressibility effect has an effect to move the flow separation point backward and to delay a reattachment of separated shear layer on the airfoil. These effects reduce the lift and the maximum lift-drag ratio.