The dark conductivity in poly (phenyl sulfone) was studied. Undoped and doped films by BF4- in chloroform solution, prepared by cast method was investigated in the temperature range (300-430 degreesK). The dark conductivity was measured in Al/poly (phenyl sulfone)/Al sandwitch structure. The measurements were performed on poly(phenyl sulfone) samples at three different thicknesses. Some temperature dependent anomalies in the electrical conductivity changes of the poly(phenyl sulfone) samples corresponding to the second order transitions were observed.