The surface morphology of polystyrene (PS) before and after u.v.-irradiation was studied by means of Atomic Force Microscopy (AFM). The u.v.-irradiation of PS sample doped with poly(methyl methacrylate) caused distinct changes in surface morphology. The nanometer-scale structures of the rod-like shape bumps of diameter of 300 nm and the height of 75 nm were created. We also showed that the very small forces of 0.2 nN are enough high to modify the surface of PS samples.