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Purpose: This study aimed to analyze the impact of different biopsy protocols on the rate of mosaic blastocysts. Methods: This is a retrospective cohort study which included 115 cycles with pre-implantation genetic testing for aneuploidy (PGT-A). Two groups were allocated based on the biopsy protocols: method 1 group, the zona pellucida (ZP) was drilled on day 3 embryos followed by trophectoderm (TE) biopsy; and method 2 group, the ZP was opened on day 5 or 6 blastocysts followed by TE biopsy. All biopsy samples were assessed using next-generation sequencing (NGS) at a single reference laboratory. The euploid, aneuploid, and mosaic blastocyst rates and clinical outcomes were compared. Results: The mosaicism rate in the method 1 group was 19.58%, significantly higher than the method 2 group (8.12%; P < 0.05). No statistically significant difference was observed in euploid, aneuploid blastocyst rates, and clinical pregnancy rates between the two groups. Logistic regression analysis indicated that the biopsy protocols were independently associated with the mosaicism rates among all the variables. Conclusions: The present study showed that different biopsy protocols may have an impact on the mosaic blastocyst rate. ZP opening on day 3 combined with TE biopsy might increase the incidence of mosaic blastocysts. [ABSTRACT FROM AUTHOR]