The work deals with crystallization of photodegraded polypropylene containing various amounts of β-nucleating agent based on N,N -dicyclohexylnaphthalene-2,6-dicarboxamide. Compression-moulded samples were irradiated by UV-light, melted and subsequently non-isothermally crystallized. The results showed that the crystallization temperature decreased with increasing irradiation time. The irradiation caused the splitting of crystallization exotherms into two peaks indicating two crystallization mechanisms. The presence of β-nucleating agent in the material suppressed the peak splitting; the higher was the amount of nucleating agent in the sample, the later was the splitting observed.