Nanoindentation tests were carried out to measure the elastic modulus of rat whisker, which is used as a high-acuity sensor for exploring the world and discriminating object distance, size and surface texture. The measured load-depth curves show that the biomaterial of rat whisker exhibits obvious visco-elastic characteristic, such as load relaxation and displacement creeping. The measured indentation modulus of rat whiskers decreases with indentation depth at the same location. The mean value of the measured indentation moduli of 24 major whiskers varies from 0.33 GPa to 4.92 GPa. The elastic modulus is independent of the freshness of the whisker sample. It is also found that the length and diameter of whiskers have no direct relationship to the indentation modulus at the base. Based on the measured elastic modulus, the bending stiffness at the base of a whisker is predicted in the range of 0.58-134.79 mN mm(2) and the rotational stiffness at the middle of a whisker is within 0.06-10.93 mN mm/rad. These results can be used to study the mechanical behavior of the rat whisker sensor system. (C) 2013 Elsevier Ltd. All rights reserved.