Arsenic is an environmental toxicant. The association of gestational arsenic exposure with adverse pregnant outcomes remains controversial. This study was to investigate the association of serum As level with adverse pregnant outcomes in a large Chinese cohort population. Total 3194 mother-and-infant pairs were recruited from the China-Anhui Birth Cohort Study. Maternal serum arsenic (As) concentration was measured using hydride generation-atomic fluorescence spectrometry. Subjects were divided into L-As group and H-As group in accordance to the 75th percentile of serum As concentration. The associations of serum As level during gestation with adverse pregnant outcomes were analyzed. The incidence of small-for-gestational-age (SGA) newborns was elevated in H-As group compared to L-As group (9.9% vs 7.6%, P = .044). After controlling confounders and stratified analysis, the adjusted OR for SGA was significant only in girls with H-As but not in boys. Moreover, the incidence of preterm delivery (PTD) was elevated in H-As group compared to L-As group (7.0% vs 4.8%, P = .016). Further analysis found that the adjusted OR for moderate-to-late PTD was 1.47 (95%CI: 1.03, 2.09; P = .034) in H-As group as compared with L-As group. These results indicate that maternal serum As level during gestation is positively associated with adverse pregnant outcomes.