A recent study found that gestational serum Pb concentration is associated with an increased risk of preterm birth. The purpose of this study was to analyze whether gestational Pb exposure elevates risk of small-for-gestational-age (SGA) births in a Chinese population. In the present study, total 3125 mother-infant pairs were recruited from the China-Anhui Birth Cohort Study (C-ABCS). Pb concentration in maternal serum was detected by GFAAS. All subjects were classified into three groups according to the tertile division of serum Pb concentration: L-Pb (low-Pb, < 1.18 μg/dl), M-Pb (medium-Pb, 1.18–1.70 μg/dl), and H-Pb (high-Pb, ≥ 1.71 μg/dl). There was no difference on birth length, head circumference and chest circumference among different groups. The rate of SGA was 6.2% in subjects with L-Pb, 8.7% in subjects with M-Pb, and 10.1% in subjects with H-Pb, respectively. The adjusted OR of SGA was 1.45 (95%CI: 1.04, 2.02; P = 0.03) in subjects with M-Pb and 1.69 (95%CI: 1.22, 2.34; P = 0.002) in subjects with H-Pb. Interestingly, the rate of SGA infants was elevated only in subjects with H-Pb in the first trimester (adjusted OR: 2.13; 95%CI: 1.24, 3.38; P = 0.007). Collectively, high serum Pb level in the first trimester is associated with an elevated risk of SGA infants.