Polypropylene was irradiated with 1 2 C ions of 3.6 and 5.4MeV energies in the fluence range of 5x10 1 3 -5x10 1 4 ions/cm 2 using 3MV tandem accelerator. Ion penetration was limited to a few microns and surface modifications were investigated by scanning electron microscopy. At the lowest ion fluence only blister formation of various sizes (1-6μm) were observed, but at higher fluence (1x10 1 4 ions/cm 2 ) a three-dimensional network structure was found to form. A gradual degradation in the network structure was observed with further increase in the ion fluence. The dose dependence of the changes on surface morphology of polypropylene is discussed.