This prospective study evaluated human milk and serum antirotavirus antibody concentrations following maternal rotavirus immunization. Postpartum women (33) were randomized into 3 groups and received a single oral dose of rhesus rotavirus monovalent reassortant vaccine (10(4) pfu), tetravalent vaccine (10(4) pfu), or placebo. Milk (secretory [s] IgA) and serum (IgA and IgG) specimens were tested for antirotavirus isotype-specific antibody. Sera also were tested for G1- to G4-specific antibody. Prevaccine milk and serum isotype-specific antibody concentrations were not significantly different in the 3 groups. Postvaccine sIgA log titers were significantly greater in the 2 vaccine groups than the placebo group (P = .002). Mean log10 titers at 1 week were 2.1 (95% confidence interval [CI], 2.0-2.3) in the 2 vaccine groups and 1.7 (95% CI, 1.5-1.9) in the placebo group. Milk titers did not differ between vaccine groups. There was no difference in reactogenicity between groups. The significantly higher milk concentrations of antibody to rotavirus in postpartum women who received rotavirus immunization persisted for 4 months.