The effect of air humidity on oscillatory flow around the NACA 0012 airfoil was investigated experimentally at Mach number M=0.71 and airfoil angle of attack a=8.5''. The background tlow oscillations were produced by a rotating rectangular plate placed downstream of the airfoil. The generated oscillation frequencies were in the range from 0.5 up to 1.5 of the buffet frequency. The presented results shown that the normal aerodynamic force variations strongly depend on the excitation frequency and reach a maximum value at frequencies typical to the buffet. The increase of the air humidity leads to considerable diminishing of the aerodynamic force variation.