Using the photoelastic technique of stress freezing, the rotating discs with a keyway are investigated under centrifugal forces. Disc models with keyways of various radius of curvatures of the corner are prepared. The preliminary experiment for rotating concentric circular ring is conducted in advance and the results are compared with the theoretical solutions. The stress concentration at the corner of the keyway is observed and the stress concentration factors are summarized with respect to the radius of curvature of the corner of the keyway. The optimum shape of the keyway will be deduced from the experimental results.