Aim: This study for the first time in Mwanza, Tanzania aimed at determining seropositivity of mumps virus in school aged children who are targeted for vaccination. Study Design: Cross-sectional study. Place and Duration of the Study: This study was conducted in the city of Mwanza from July to September 2018. Despite being common with reported associated complications in many resource limited countries, there is scarcity of information on its epidemiology in Tanzania. Methodology: We enrolled 440 school children aged 6-12 years. Data was collected using a pre-tested structured data collection tool. Blood samples were collected, and sera were used for detection of mumps virus antibodies by indirect enzyme linked immunosorbent assay (ELISA). Data was analyzed using STATA version 13, 2013. Results: The median age of enrolled children was 9(IQR: 8-11) years. The seropositivity of mumps IgG antibodies was found to be 94(21.4%, 95% CI: 17.5-25.1) while that of IgM was 1 (0.23%, 95% CI: 0.02-0.6). By multivariable logistic regression analysis, residing in rural areas (OR: 2.28, 95% 1.42-3.36, P=0.001) and age >10 years (OR: 1.67, 95% CI: 1.03-2.7, P=0.036) independently predicted mumps IgG seropositivity. Conclusion: A significant proportion of young children in urban areas of the city of Mwanza are susceptible to mumps virus infection indicating the need to generate more data across the country so as to institute appropriate control measures including measles, mumps and rubella (MMR) vaccination programme.