Three dimensional photo-elastic analysis of the marine propeller blade was carried out to clearify the stress characteristics of the blade subjected to hydrodynamical forces. Stress distributions in the blade obtained from photo-elastic method were discussed comparing with the calculated ones by Taylor's method and Shoenherr's method. Tension stress patterns on the face side in the cross sections showed considerably different features from calculated ones, while compression stresses on the back side nearly agreed with calculated ones. The maximum stress on the face side in cross sections was observed in the vicinity of the nearly half point of the blade width. These features are not always completely explained from the influence of inclined neutral axis in bending, which is comfirmed also in our photo-elastic observations, and the influence of propeller pitch on the stress patterns was not outstanding in this range of the pitch ratio 0.6521.078.