Nanoindentation is a useful technique to measure hardness as well as elastic and timedependent plastic properties of materials with nanometer resolution. The measurement of elastic modulus of polymeric materials remains challenging due to their viscoelastic behavior. Clay reinforced nylon6 nanocomposites are found to have great improvement in the elastic modulus and tensile strength due to exfoliated hybrid structure. However, its mechanical properties have not been well investigated. In the present study, hardness and elastic modulus of nylon6-5wt%clay nanocomposites were investigated using nanoindentation. Creep effects of the nanocomposites on the unloading stiffness, which directly relates to the elastic modulus, were studied under various unloading rates and holding periods. It was found that the elastic modulus and hardness of nylon6-5wt%clay nanocomposites increased by 58% and 80%, respectively, as compared to pure nylon6. Experimental results for both polycarbonate and nylon6-5wt%clay nanocomposites showed that loading rate had no significant effects on the unloading stiffness. However, stiffness decreased to more consistent values after longer holding periods (more than 30 sec) and at faster unloading rates. The results indicated that creep behavior of the polymers affects the measurement of the unloading stiffness and may possibly overestimate the elastic modulus. Errors in the stiffness measurements from nanoindentation could be minimized with appropriate loading, unloading and holding conditions.