Abstract Polystyrene composite films with different content of C60 + C70 fullerene mix have been obtained from o-xylene solutions. The mass fraction of fullerene was varied from 0.01 to 0.1 mass%. The glass transition temperatures and specific heat capacities in range of 293–423 K have been determined for the films by DSC method. The plasticization of the polymer is observed in thermal properties of the films under influence of small fullerene additions. The values of Tg and CP decrease and thermal coefficient of heat capacity b increase as fullerene content increases up to 0.02 mass%. The effect of interaction between polymer and fullerene molecules on thermal properties becomes evident at higher fullerene content in range from 0.02 to 0.1 mass%. At this the values of Tg and CP increase and b coefficient decrease with increasing content of fullerene. Concentration dependence of CP and b values is less steep for polymer composite films in elastic state at temperatures above Tg. Molecular interactions in t...