Background: Reducing maternal morbidity and mortality is a global priority which is particularly relevant to developing countries like Ethiopia. One of the key strategies for reducing maternal morbidity and mortality is increasing institutional delivery service utilization of mothers under the care of skilled birth attendants. Objective: To assess skilled institutional delivery service utilization and associated factors among mothers who give birth in the last one year in Mahal sayint woreda, South Wollo zone, North East Ethiopia. Method: A community-based cross-sectional survey was conducted among mothers who had delivered in the previous one year. Data were entered in to Epidata 3.1 and analyses were made by using SPSS version 20. Tables and graphs were used to present descriptive analysis. A bivariate logistic regression analysis was done to see the crude association between independent and outcome variables. After that multiple logistic regression model was done and significant statically association were considered based on adjusted odd ratio included in 95% confidence interval at P-value less than 0.05. Result: A total of 298 mothers were interviewed from 301 total sample sizes which gives 99% response rate. Of the total respondents, 251(84.2 %) gave birth at home due different reasons. Among these reasons ninety (30.3%) of the mothers said having closer attention from family members and 23.8% previous home delivery experience. Age, educational status of the mother, income and number of antenatal care visit were found to be significantly associated with the institutional delivery service utilization in multivariable logistic regression analysis. Conclusion: Majority of the respondents had a history of home deliveries due to many reasons so that attention should be given by health professionals and Mahal sayint woreda health office.