In this paper, the effects of delamination on critical buckling load failure of unidirectional E-glass/epoxy composite laminated plate consisting of delamination at the middle of the mid plane were studied. Experimental work was carried out to determine the buckling load for rectangular composite plates consisting of delamination for various aspect ratios ranging from 0.5 to 3. Stitched and unstitched laminates were prepared by introducing inplane delamination at the mid of the mid plane using Teflon film. These specimens were made with unidirectional fiber of orientation of (0o/-45o/45o/90o)s with single inplane delamination at the mid of the mid plane of through width and various lengths of 130 mm and 50 mm. The Plates were made to buckle experimentally by simply supporting the top and bottom edges, and sides were kept free. Buckling load has been found from the graph. The critical buckling load is found to be increased in the stitched laminates when compared with unstitched laminates and is decreased in both stitched and unstitched laminates as the aspect ratio increases. The experimental results were validated by using commercial finite element software of ANSYS.