The stress distribution in a bolted joint and the pressure distribution on the bearing surface of a nut have been examined by three-dimensional photoelastic experiment. As a result of this experiment : (1) The experiment shows that the stress distribution in a bolted joint has axially unsymmetric, since the screw part has an axi-unsymmetrical shape. (2) The pressure distribution on the bearing surface of a nut has an unsymmetry corresponding to that stated above. (3) It can be seen that the screw part of the bolted joint is acted upon by the bending moment due to the unsymmetric pressure distribution. (4) In the cases of a nut having some part without thread the following fact has been observed. The peripheral portion of the nut can be bear the load pressure which has uniform distribution in all directions of circular angles.