Abstract Objective: To evaluate associations between early pregnancy 25-hydroxyvitamin D (25[OH]D) concentrations and antepartum depression and anxiety symptoms and potential modifiers thereof. In a pregnancy cohort (N=498), we examined cross-sectional associations of early pregnancy (mean=15.4 weeks gestation) serum 25[OH]D concentrations and depression and anxiety symptoms. Symptoms were measured using Depression, Anxiety, and Stress Scales (DASS-21) and Patient Health Questionnaire Depression Module (PHQ-9) instruments. Regression models were fit and effect modification by prepregnancy body mass index and leisure-time physical activity (LTPA) were assessed using interaction terms and stratified analyses. Mean 25[OH]D concentration was 34.4 ng/mL. Approximately 12% had "moderate" anxiety (score ≥ 10) and depression (score ≥ 10) symptoms by DASS-21 Anxiety and PHQ-9 instruments, respectively. A 1 ng/mL lower 25[OH]D was associated with 0.043 and 0.040 higher DASS-21 Anxiety and PHQ-9 Scores (p-values=0.052 and 0.029, respectively). Participants in the lowest quartile of 25[OH]D (<28.9 ng/mL) had 1.11 higher PHQ-9 scores than those in the highest quartile (≥ 39.5 ng/mL, p<0.05). However, associations were attenuated and statistically insignificant in fully adjusted models. Inverse associations of 25[OH]D with depression symptoms were significant among participants who reported no LTPA, but not among women who reported any LTPA (interaction p=0.018). Our study provides modest evidence for inverse cross-sectional associations of early pregnancy maternal vitamin D concentrations with antepartum depression symptoms. We also observed that these associations may be modified by physical activity.