In optical storage technology, gratings consisting of curved grooves have been formed in disks to record data and in integrated optical pickup devices to read signal. Groove parameters, such as pitch, width, and depth, can be inspected by the light diftraction method. Diffraction patterns are usually analyzed without considering the curvature of grooves. A model is developed to examine diffraction patterns of curved grooves. Theories for uncurved and curved grooves are compared. An optical inspection system is developed. Experimental results are analyzed and compared with theories.