Abstract: Stitching can improve the delamination resistance of traditional 2D laminates obviously. However, it may result in the degradation of other mechanical properties due to the creation of resin pockets or the breakage of in plane fibers. In this paper, the effects of through the thickness stitching on compression strength, interlaminar shear strength, Mode I and Mode II fracture toughness, impact damage resistance of composite laminates and compression after impact (CAI) strength were investigated experimentally. Specimens with varying stitching density, stitching direction, thread type and thread diameter are studied. The results show that stitching significantly improves G IC  and G IIC  of laminates; with increase in stitching density, interlaminar shear strength and CAI strength increase rapidly, and the impact damage area decreases slightly; however, they are not closely related to the thread diameter. In addition, the mechanisms by which stitching increases the CAI strength and fracture toughness were discussed.