In Mozambique, as in many sub-Saharan countries, measles remains a public health problem. We conducted cross-sectional surveys in which we assessed measles-specific antibodies in serum and breast milk by plaque reduction neutralization (PRN) assay and measles secretory IgA in breast milk by enzyme-linked immunosorbent assay. A total of 151 persons < 1 month to 23 years of age were surveyed; 81 (53.6%) of 151 had PRN titers equal to or above the protective level (>/= 200 mIU/mL). We found many serosusceptible persons, including 20.5% in whom no PRN antibody was detected. Almost all (96%) infants 6-8 months of age had non-protective PRN titers. Overall, 20.7% (6 of 29) of persons known to have received measles vaccine had non-protective titers. The geometric mean titer (GMT) of breast milk PRN antibodies was 41.6 mIU/mL (95% confidence interval [CI] = 34.0-51.0 mIU/mL) and the secretory IgA GMT was 227.6 (EU/mL) (95% CI = 179.1-289.1 EU/mL). The PRN titers of breast milk tended to increase with age. A notable proportion of the population in Manhiça, Mozambique apparently remains susceptible to clinical measles despite recent mass vaccination campaigns.