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Per- and polyfluoroalkyl substances (PFAS) are believed to impair early neurodevelopment and disrupt thyroid hormone (TH) levels. However, there are limited epidemiological data on the neurodevelopmental effects in infancy of prenatal PFAS exposure and the potential mediating effects of TH. To evaluate potential associations between prenatal PFAS exposure and early neurodevelopmental deficiencies, and assess mediator effects of TH. From 2010 to 2013, 274 mother-infant pairs were recruited to the Laizhou Wan Birth Cohort in China. Ten PFAS and five TH were measured in cord serum. Developmental quotient (DQ) from 5 domains (adaptive, social, language, gross and fine motor) was assessed using Gesell Developmental Schedules for each child at 1 year of age. The associations between PFAS and DQs were evaluated using multivariable linear regressions. TH-mediated effects of PFAS on DQs were calculated by mediation analyses. Among our study population, PFAS exposures were common and associated with DQ decrement in infants. For each 10-fold increase in PFBS concentrations, gross motor and adaptive DQ decreased by 8.56 (95%CI: −15.15, −1.97) and 5.87 (95%CI: −8.07, −3.67) points, respectively. TSH mediated 12.90% of the association of PFBS with gross motor DQ and FT4 explained 19.63% of the association of PFBS with adaptive DQ. The negative association was also found between PFHxS exposure and gross motor DQ (β = 8.14, 95%CI: −15.39, −0.98). PFBS and PFHxS were negatively associated with early neurodevelopment, especially consistent in gross motor domain. The associations were partly explained by TSH and FT4. • The relationship between PFAS exposure, thyroid hormones and infant neurodevelopment were assessed in a Chinese birth cohort. • Prenatal PFHxS and PFBS exposure were associated with lower gross motor DQ, especially in males. • TSH and FT4 partly mediated the association of PFBS with DQ in several neurodevelopmental domains at 1 year of life. [ABSTRACT FROM AUTHOR]