OBJECTIVE: To investigate the effect of blastocyst quality on the strategy of single blastocyst transfer in frozen-thawed cycles. METHODS: A retrospective analysis was performed in Reproductive Medicine Center, Maternal and Child Health Hospital of Guangxi Zhuang Autonomous Region on clinical data of single frozen-thawed blastocyst transfer cycles from January 2008 to December 2013. All cycles were divided into four groups (AA, AB/BA, BB, BC/CB) according to the blastocyst score, then the clinical outcomes were compared between groups. And on this basis, the clinical outcomes were further explored when the group of outcomes with single blastocyst transfer wasn't ideal, which would diverted to transfer two blastocyst. RESULTS: In single frozen blastocyst transfer cycles, the clinical pregnancy rate of each group with the blastocyst scored AA, AB/BA, BB, BC/CB were 61.4% (470/765), 51.2% (330/645), 40.5% (407/1 005), 22.9% (60/262), live births rate in each group were 52.2% (399/765), 41.2% (266/645), 30.4% (306/1 005), 13.7% (36/262), and the abortion rate were 13.6% (64/470), 16.7% (55/330), 21.4% (87/407), 35.0%(21/60), separately. This showed that the clinical pregnancy rate and live births rate decreased significantly with the decline of blastocyst quality (P<0.01), but the abortion rate showed significant upward trend (P<0.01). When single blastocyst scored ≥BB grade transferred, an acceptable clinical pregnancy rate (>40%) and live births rate (>30%) could be obtained, however, the clinical pregnancy rate of 22.9% and live births rate of 13.7% could only be acquired when blastocyst scored BC/CB only transferred one embryo, which significant lower than those of each group scored ≥BB grade (P<0.01). So, after that, the blastocyst scored BC/CB were further divided into two groups (single blastocyst transferred versus two blastocyst transferred) to investigate, then the result showed that the clinical pregnancy rate [22.9% versus 38.5%(67/174),P<0.01] and live births rate [13.7% versus 30.5%(16/67),P<0.01] were significantly increased in the group of two blastocyst transferred compared with the group of one blastocyst transferred, and the abortion rate was also significantly decreased from 35.0% to 17.9% (12/67;P<0.05). So when two blastocyst scored BC/CB were transferred, the clinical outcomes were similar to the group of one blastocyst scored BB transferred (P>0.05). CONCLUSIONS: Of single blastocyst transfer in frozen-thawed cycles, the clinical pregnancy rate and liver births rate showed significant upward trend, but the abortion rate showed significant downward trend, with the decline of blastocyst quality. When the blastocyst scored ≥BB grade, the single blastocyst transfer could be considered to be performed.