〔Abstract〕 Objective To compare the clinical outcomes of double D5, D5+D6 and double D6 blastocysts transfer, meanwhile, explore the effectiveness and safety of D5+D6 blastocysts transfer protocol. Methods A retrospective analysis of 2 180 cycles ofin vitrofertilization/intracytoplasmic sperm injection-embryo transfer(IVF/ICSI-ET) in reproductive medicine center of our hospital. All cycles were divided into three groups in accordance with the different development days of blastocysts: double D5 group(n=1 201), D5+D6 group(n=205) and double D6 group(n=774). Results The biochemical pregnancy rates, clinical pregnancy rates and multiple pregnancy rates in the D5+D6 group were higher than those in the double D6 group(P<0.001), and lower than those in the double D5 group(P<0.001). Double D5 group had higher early pregnancy loss rate compared with D5+D6 group and double D6 group(P>0.05,P<0.05, respectively). The ectopic pregnancy rate in the D5+D6 group was lower than that in the double D5 group and the double D6 group, but there was no significant difference(P>0.05). Conclusion D5+D6 blastocysts transfer as a new protocol can obtain good clinical outcomes.