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Determination of mechanical properties by nanoindentation in the case of viscous materials A mechanical model based on a generalized Kelvin-Voigt model has been developed to explain and fit the nanoindentation curves realized on three amorphous polymers (PC, PMMA and PS). This model includes the responses of quadratic elastic (spring), viscoelastic (two Kelvin-Voigt elements), plastic (slider) and viscoplastic components (dashpot). It is able to fit nanoindentation curves during loading, unloading and hold time periods. With the values of the model parameters and the value of the contact area calculated with the Oliver and Pharr method, it is possible to calculate the values of the mechanical properties of the polymers. A good agreement is found between these values and those obtained with conventional methods.