- Near the temperature of 260 K, C 60 crystal is known to undergo a first order phase transition, associated with changes in molecular rotations. The present paper reports the effect of the crystalline structure and impurity content of C 60 thin films on their structural behavior near this phase transition. Polycrystalline C 60 films with different grain sizes and oxygen content were obtained by varying the conditions of their vacuum deposition and post- grown exposure. Temperature-resolved X-ray diffraction in the range 300–15 K was used to determine the lattice parameter and its changes near the phase transition temperature. Decrease in grain sizes and increase in oxygen content of the films are found to lead to a gradual reduction in the discontinuity in lattice parameter and the transition temperature.