The main purpose of this investigation is to characterize experimentally the interlaminar shear strength of cross-ply and quasi-isotropic E-glass/epoxy composites by the four point short beam test. ASTM D2344-three point short beam strength test results and the four point short beam strength test results are compared. To determine the details of the four point short beam test, the effects of support span to thickness ratio, load span, ply number, width and fibre orientation on the interlaminar shear strength are investigated. According to the test results the four point short beam test is more advantageous and more convenient than the three point short beam test because of the better load distribution and higher support span to thickness ratio. It is concluded that the support span to thickness ratio should be 8 to obtain pure interlaminar shear failure. The distance between the two loading cylinders should be one half of the support span instead of one third of the support span. When measuring the interlaminar shear strength for E-glass/epoxy laminates, the ply number and the width of the specimen should be chosen carefully.