Background: Maternal mortality is a major public health problem in low- and middle-income countries. Evidence shows that adequate health service utilization and empowering the women on decision making about own health to have positive impact on improving maternal health care utilization and key to tackle maternal morbidity and mortality Objectives: The objective of this study was to assess the women’s autonomy of deciding on their maternal health service utilization &associated factors in Ambo Town, Ethiopia. Methods: Community based cross-sectional study was conducted on 381 women of having under five children from March 3- April 3 2018. Face to face interview was carried out to collect data using structured questionnaires. Multi stage sampling method was used to get required sample. The collected data was entered to Epidata 3.1 and transported to SPSS version 22 for data analysis. Descriptive statics, binary and multiple logistic regression analysis was conducted to identify factors associated with autonomy of women. The independent variables having P value <0.05 in multiple logistic regression analysis was taken as significant association and reported using p-value and adjusted odd ratio. Result: Out of 381 women, more than half (55.6%) had higher autonomy of decision making regarding their maternal health service utilization. Parity; number of living children; Educational status of women; exposure to media; marriage type and age at marriage were significantly associated with women’s autonomy. Conclusion: women’s autonomy of decision making on their maternal health service utilization plays a central role on reduction of maternal mortality and morbidity and still needs strong focus. Socio-demographic and socio-cultural factors were found to influence women’s autonomy.