<p>Instrumented indentation test (IIT), with basic assumption of perpendicularly penetrating into sample surface, is an effective technique to determine the elastic modulus and hardness. However, tilt angle of sample is a common phenomenon in IIT, which may decrease the accuracy of determined elastic modulus and hardness. In this work, both finite element simulations and experiments were conducted to quantitatively examine the influence of sample’s tilt angle on measuring elastic modulus and indentation hardness by IIT with Berkovich and Vickers indenters. It was found that the sample tilt results in an overestimation of elastic modulus and hardness due to overestimation of the initial unloading stiffness and underestimation of the projected contact area. The rotation angle is a minor factor when the tilt angle is no more than 2°. The sample’s tilt angle is recommended to be less than 2°. This work provides guidance in instrumented sharp indentation test.</p> Graphic abstract <p></p>