Objective: To investigate the serum and milk in active-smoking and nonsmoking mothers, and their infants’ insulin-like growth factor-I (IGF-I) and insulin-like growth factor binding protein-3 (IGFBP-3) levels. Design and Setting: A cohort study conducted at a tertiary medical center. Subjects: Forty-four mothers (age range: 21–34 years) and their newborns (7 days old) were enrolled in the study. Mothers were interviewed and classified according to their smoking status into one of two groups: the active-smoking mothers (n = 21) and the nonsmoking mothers (n = 23). Results: There was no difference noted in either IGF-I, IGFBP-3 or IGF-I/IGFBP-3 ratios in serum and milk of mothers, and their infants’ serum samples according to maternal smoking. Conclusion: This study demonstrated that maternal smoking (5–10 cigarettes/day) did not influence the maternal and infant serum levels of IGF-I and IGFBP-3 as well as the breast milk levels of these peptides.