Avoiding aneuploid embryo transfers has been shown to improve pregnancy outcomes in patients with implantation failure and pregnancy loss. This retrospective cohort study aims to analyze the correlation of time-lapse (TL)-based variables and numeric blastocyst morphological scores (TLBMSs) with different mosaic levels. In total, 918 biopsied blastocysts with time-lapse assessments at a uniform time-point were subjected to next-generation sequencing–based preimplantation genetic testing for aneuploidy. In consideration of patient- and cycle-related confounding factors, all redefined blastocyst morphology components of low-grade blastocysts, that is, expansion levels (odds ratio [OR] = 0.388, 95% confidence interval [CI] = 0.217–0.695; OR = 0.328, 95% CI = 0.181–0.596; OR = 0.343, 95% CI = 0.179–0.657), inner cell mass grades (OR = 0.563, 95% CI = 0.333–0.962; OR = 0.35, 95% CI = 0.211–0.58; OR = 0.497, 95% CI = 0.274–0.9), and trophectoderm grades (OR = 0.29, 95% CI = 0.178–0.473; OR = 0.242, 95% CI = 0.143–0.411; OR = 0.3, 95% CI = 0.162–0.554), were less correlated with mosaic levels ≤20%,