The effect of the adhesive thickness on the overall strength of single lap joints made by lightweight aluminum alloy was experimentally studied. The relation between the overall strength and the adhesive thickness is influenced by some intrinsic characteristics of adhesives,one of which is the adhesive toughness addressed by the present study. The results show that the variation of overall strength corresponding to relatively ductile adhesive is more remarkable compared to that corresponding to relatively brittle adhesive,especially in the comparatively small adhesive thickness range. When the adhesive thickness is larger than the critical thickness,the overall strength of the single lap joints appears equal to the bulk shear strength of the adhesives. The present experimental results agree with the previous model prediction.