Three ICSI methods were examined to determine their clinical efficiency and the mechanisms of oocyte damages. The volumes of cytoplasm aspirated into the ICSI pipette at oolemma breakage, the sizes of the broken areas in the oolemma and the rates of oocyte lysis and fertilization after sperm injections were compared. The three ICSI methods were Conventional-ICSI (CI), Conventional Piezo-ICSI (CPI) (using standard 1 µm thickness micropipettes) and Improved Piezo-ICSI (IPI) (using ultra-thin 0.5 µm thickness micropipettes). The volumes of cytoplasm aspirated into the ICSI pipette at oolemma breakage in CI, CIP and IPI were 2792 ± 952, 0 ± 0 and 0 ± 0 µm³, respectively. Significantly, the greatest volume of cytoplasm aspirated into the ICSI pipette (P<0.0001) was observed in the CI method. The sizes of the broken areas in the oolemma in CPI and IPI were 18 and 8 µm², respectively. The rates of lysis and fertilization after CI, CPI and IPI were 10, 5 and 1%, and 78, 79 and 89%, respectively. Significantly, the lowest lysis rate (P<0.0001) and highest fertilization rate (P=0.0021) were obtained by the IPI method. The results show that the IPI method is the best ICSI method as it reduced the broken area in the oolemma at sperm injection, and resulted in the lowest oocytes lysis and highest fertilization rates.