Pyrite thin films have been grown by sulphuration of Fe thin films and their Seebeck coefficient has been measured as a function of the sulphuration temperature in the range 370-720 K. Films appear to be p-type (positive Seebeck coefficient) for sulphuration temperatures higher than 450 K The evolution of the coefficient with the sulphuration temperature has been qualitatively correlated with the crystallization process that the films suffer on increasing that temperature. According to our analysis, the highest value of the Seebeck coefficient obtained in our measurements (S ≈ 80 µV K −1 ) should correspond to non-stoichiometric crystallized pyrite films formed by spheroidal grains.