A stereoscopic image display including an image displaying unit and an optical grating is provided. The image displaying unit has a black matrix and pixels surround by the black matrix, and each pixel has a width P in a first direction. The optical grating is disposed corresponding to the image displaying unit, wherein the optical grating comprises a plurality of constitutional groups arranged in the first direction. Each of constitutional groups comprises a plurality of slits having the same width W to expose the corresponding pixels, the width P of pixel and the width W of slit satisfy a specific relationship, so as to reduce the morie phenomenon and provide excellent stereo image quality.