An experimental study was performed to evaluate the roughness effect on the determination of hardness and Young´s modulus of ceramic materials from nanoindentation tests. Several specimens polished at various stages were tested at different peak load values. Local roughness measurements have been done by means of atomic force microscopy. Results indicate that roughness and size effects are joined. Proportional Specimen Resistant Modified model (PSRM) was applied to avoid the scale effect, isolating the roughness influence. Indentations where the average roughness-elastic displacement ratio is lower than a critical value are needed to get consistent results.