Although pyrethroid insecticides are widely used, little is known about potential adverse effects on fetal growth. Participating 454 mother-infant pairs were recruited from a prospective birth cohort in rural northern China between September 2010 and 2012. We measured five non-specific pyrethroid metabolites in maternal urine at delivery and examined their association with birth outcomes including birth weight, length, head circumference, and gestational duration. The creatinine-adjusted medians of pyrethroid metabolites in urine were 0.51 μg/g for cis-DCCA, 0.65 μg/g for trans-DCCA, and 0.68 μg/g for 3-PBA. The pregnant women had substantially higher levels of urinary pyrethroid metabolites compared with those reported in developed countries. A increase in total (the sum of cis-DCCA, trans-DCCA, and 3-PBA) but not individual urinary metabolite levels was associated with a decrease in birth weight (adjusted β=-96.76 g per log10 unit increase, 95% confidence interval=-173.15 to -20.37). No associations were found between individual or total metabolite levels and birth length, head circumference, or gestational duration. We report an adverse association of prenatal exposure to pyrethroids as measured by urinary metabolites with birth weight. More studies are warranted in China given the relatively high levels of urinary metabolites in our study population.