Aims: Mumps infection and its complication remain under recognized public health problem in Tanzania, as there are no national screening program and sero-epidemiological surveys. This makes it difficult to devise control interventions including administration of vaccinations. We therefore determined the Sero-prevalence of Mumps among Unvaccinated Children Attending Regional Referral Hospitals in Dar es salaam, Tanzania. Study Design:  A hospital based cross-sectional study. Place and Duration of Study: Outpatient departments of three regional hospitals in Dar es Salaam Tanzania: Amana, Mwananyamala, and Temeke hospitals, from March to June 2021. Methodology: Three hundred and sixty children aged 1 - 16 years were included in the study. A structured questionnaire was used to collect participants' information. Serum samples were tested for mumps immunoglobulin G antibodies using an enzyme linked immune-sorbent assay. Proportions were used to describe children's social demographic and clinical characteristics, and binary logistic regression was used to estimate the odds of exposure to mumps virus. A p-value < 0.05 was considered statistically significant. Results: The mean age was 7.6 ± 4.1, half of them were females. More than three quarters (77%) of the children had Mumps Immunoglobulin-G. Mumps sero-prevalence among under-fives was 58.8%, among 5-8 years was 80%, 9-12 years was 86% and for 13-16 year was 88%. Compared to under-fives, children in the ages of 5-8, 9-12 and 13-16 had four times. (OR 4.19 95% CI 1.49-11.7), five times (OR 5.84 95% CI 1.89-18.12) and six times (OR 6.00 95% CI 1.63-21.43) higher odd of mumps exposure respectively. The number of siblings in the house, going to school, and previous history of parotid gland enlargement were not associated with mumps sero-positivity. Conclusion: The mumps virus is circulating in a high proportion among children in Dar es Salaam and the likelihood of exposure increases with age.