Results of an investigation of the effect of surface tilt in range of 0-6 deg on nanoindentation measurements under Berkovich indenter at different loads made on copper and glass surfaces are presented and discussed. It was found that: (1) measured hardness increases for tilt angle >3 degand this increase is about 12% at 6 degfor both samples at all applied loads, (2) the overestimation in hardness is due to the increase of projected contact area A with the tilt angle, but the theoretical contact area A described by the traditional analytical area function leads to lower change in the hardness than the experimental one up to about 5% may be attributed to the horizontal deflection of the stem holding the indenter, and (3) indentation modulus E is more sensitive to the tilt for glass than copper and the sensitivity in the values of E at a given tilt angle increases with decreasing indention load.