Longitudinal associations with psychological factors modifying the effects of chemicals have not been sufficiently explored in epidemiologic studies. Our birth cohort study is the first to assess the associations between prenatal organophosphate ester (OPE) exposure and child behavior and to determine whether these associations change with pregnancy-related anxiety (PRA). Ultra-performance liquid chromatography‒tandem mass spectrometry (LC‒MS) was used to measure the tris(2-chloroethyl) phosphate (TCEP) and OPE metabolites in the 1st, 2nd and 3rd trimester urine samples. The evaluation of the behavioral development of children aged 4 years was based on the Chinese version of the Child Behavior Checklist (CBCL 1.5-5) from the main caregivers' reports. Two PRA groups (anxiety vs. nonanxiety) were identified using growth mixture models (GMMs). Generalized linear models (GLMs) and quantile-based g-computation (QGC) models were established to assess the effects of individual OPEs and a mixture of OPEs on preschoolers' behaviors stratified by PRA. Among the 1148 mother‒child pairs, GLMs revealed that, in the 1st trimester, children in the highest tertile of dibutyl phosphate (DBP) concentration presented remarkably greater behavioral problem scores than did those in the lowest tertile. First-trimester diphenyl phosphate (DPHP) was positively associated with internalizing problem scores, whereas bis(2-ethylhexyl) phosphate (BEHP) was negatively associated with behavioral problem scores. Third-trimester bis(1-chloro-2-propyl) phosphate (BCIPP) was associated with increased internalizing problem scores. Notably, positive associations between 1st trimester DBP, 2nd trimester DPHP and 3rd trimester BCIPP and behavioral problem scores were stronger among children of mothers with PRA. Using the QGC model, when the analysis was performed separately in the anxiety group, significant associations were found between the mixture of OPEs during the 3rd trimester and internalizing (β = 4.25, 95% CI: 0.24, 8.26) and total problem scores (β = 3.97, 95% CI: 0.64, 7.30). Prenatal OPE exposure may impair preschoolers' behavior, and this effect is potentially driven by PRA.