Studies have shown that thyroid autoimmunity (TAI) is associated with increased risks of adverse pregnancy outcomes. The aim of this study was to investigate the associations between TAI and embryo quality in euthyroid women undergoing in vitro fertilization or intracytoplasmic sperm injection (IVF/ICSI).This retrospective cohort study included euthyroid infertile women with and without TAI (defined as a serum thyroperoxidase concentration ≥ 34 IU/mL or thyroglobulin concentration ≥ 115.0 IU/mL) who underwent their first complete IVF/ICSI treatment cycles at a tertiary referral center between April 2016 and February 2022. Embryo quality measurements and clinical outcomes were compared between women with (TAI-positive) and without TAI (TAI-negative). The high-quality cleavage embryo rate and cumulative live birth rate (cLBR) were the primary outcomes.A total of 499 TAI-positive and 2,945 TAI-negative women were included in this study, and their mean (standard deviation) ages were 31.6 (4.5) and 30.9 (4.4) years, respectively (p = 0.001). The overall analysis showed no significant differences between TAI-negative and TAI-positive women in the high-quality cleavage embryo rate (n/N: 11,139/22,553 vs. 1,971/3,820; adjusted rate: 52.8% vs. 51.6%, p = 0.66) and cLBR (1,917/2,945 vs. 327/499; 53.4% vs. 56.2%, p = 0.31). Moreover, no significant differences were observed between TAI-negative and TAI-positive women in the rates of oocyte retrieval (35,078/51,978 vs. 5,853/8,628; 69.1% vs. 67.4%; p = 0.65), fertilization (23,067/34,197 vs. 3,902/5,728; 61.1% vs. 62.2%, p = 0.34), embryo utilization (18,233/22,553 vs. 3,156/3,820; 80.2% vs. 80.8%, p = 0.61), blastocyst formation (7,051/13,721 vs. 1,192/2,330; 48.5% vs. 48.4%, p = 0.97) and high-quality blastocysts (4,819/13,721 vs. 799/2,330; 29.9% vs. 29.4%, p = 0.73). Furthermore, no significant differences were observed between TAI-negative and TAI-positive women in the clinical pregnancy rate (1,524/2,808 vs. 248/482; 46.7% vs. 44.6%, p = 0.40), early pregnancy loss rate (156/1,524 vs. 23/248; 13.5% vs. 11.5%, p = 0.44) and live birth rate (1,338/2,808 vs. 218/482; 37.4% vs. 36.0%, p = 0.55) of the first transfer cycle.This study demonstrated that TAI in women was not associated with embryo quality or the cLBR following IVF/ICSI. Future large prospective studies are warranted to confirm these findings.