BACKGROUND: - Postnatal care is care (PNC) given to mother and new born within first 42 days of delivery. Lack of care in this period may result in disability even death of either of mother or newborn or both. The aim of this study was to determine postnatal service utilization and associated factors among women, who gave birth in the last 12 months prior to May, 2019.METHODS: Community based cross-sectional study was conducted on 420 women who had given birth prior to May 1 to June 30, 2019(study period). The 17 kebeles of Jimma town is grouped into three similar groups based on occupation of majority of population. Three kebeles were randomly selected from each group. Data was collected using a pretested structured questionnaire. Descriptive statistic, such as frequencies, proportions and means were calculated. In bivariate logistic regression variables with p-value less than 0.25 were selected for multiple logistic analyses and multiple logistic regression was conducted. Finally significantly associated variables were declared at p value less than 0.05.Result:-This study showed that prevalence of postnatal care utilization was 59.5%. Mothers who knew at least one danger signs which comes after delivery (AOR=11.5,(95%CI:5.56,22.7),who attended ANC (AOR=5.4, 95%CI:2.7,11.3 ), who get counseled to attend PNC ( AOR=14.9% CI :6.1,31.4),who attended at least primary school (AOR=2.3 ,95% CI:1.75,7.0),who did not travel more than 30 minutes to reach health facility(AOR=6.8,95% CI 3.4, 13.6 and those having more family size were more likely utilized postnatal service than their counterpartConclusions: - In this study utilization of postnatal care service was very far behind national target (which is 95% at the end of 2020, health sector transformational plan). Awareness about danger signs, educational status of the mother, counseling to attend to attend postnatal care, distance from health facility and family size were strongly associated with PNC utilization.