Experimental studies have demonstrated that cadmium exposure induces alterations on immune function, but epidemiological evidence is lacking.To examine the associations between prenatal and postnatal cadmium exposure and cellular immune responses among pre-school children.Pre-school aged children (n = 407) were followed from a prospective birth cohort study in Wuhan, China. Maternal urinary and children's plasma cadmium concentrations were measured as biomarkers of prenatal and postnatal cadmium exposure, respectively. Children's cellular immune responses were assessed by peripheral blood T lymphocyte subsets and plasma cytokines. Multivariable adjusted models were applied to estimate the associations of prenatal and postnatal cadmium exposure with T lymphocyte subsets and cytokines, and the effect modification by child gender were also examined.Maternal urinary cadmium was associated with reduced absolute counts of CD3CD4 cells (-12.45%; 95% CI: -23.74%, 0.40% for the highest vs. lowest quartile; p for trend = 0.045). Inverse associations of maternal urinary cadmium with %CD3CD4 cells and CD4/CD8 ratio were only observed among females (both p-interaction < 0.050); whereas an inverse association with absolute counts of CD3CD8 cells was only observed among males (p-interaction = 0.057). Positive associations of maternal urinary cadmium with %CD3CD4 cells, interleukin-4 (IL-4), and IL-6 were only observed among females, although there were no significant interactions. We observed no clear associations of children's plasma cadmium with T lymphocyte subsets and cytokines.Prenatal but not postnatal cadmium exposure was associated with sex-specific alterations on children's cellular immune responses.