Polythiohydantoins were synthesized by the polycondensation or polyaddition reaction of p-phenylene bisthiohydantoin with terephthal aldehyde, dinitrosobenzene, terephthaloyl chloride, p-phenylene diisothiocyanate and 2, 4-tolylene diisocyanate. For the investigation of photo-conduction in 10^-6 Torr, surface-type cell was employed to avoid the effect of space charge which was observed in sandwich-type cell. Dependence of dark-current and photo-current on the electrical field strength showed a linear relationship. The light-intensity dependences and spectral responce of illumination for photo-current were observed. The values of the slope (n) in the expression I _p =kL ⁿ were from 1.33 to 1.49 in polymers. The peaks on the response curve of photo-current were showed at ca. 500 mμ in all polythiohydantoins.