We examined whether partial thinning of zona pellucida by a LAH (laser-assisted hatching) system in ICSI could ease pressure on the egg and influence the results of subsequent embryogenesis and pregnancy rate (90 subjects, 101 cycles). ICSI was performed with and without thinning of zona pellucida in a thinning group and a control group, respectively, and the results of embryogenesis and pregnancy rate were compared between the two groups. Fertilization rate, oocyte degeneration rate, good embryo rate, and pregnancy rate in early embryo implantation were higher, though not significantly in the thinning group (80.8%, 7.5%, 66.5%, and 28.6%) than in the control group (73.0%, 9.7%, 64.6%, and 23.1%). The fertilization rate was significantly higher in the thinning group compared to the control group. Our results suggest that partial thinning of zona pellucida using a LAH system is useful in ICSI.