Maternal health service utilizations are poorly equipped, inaccessible, negligible, and not well documented in the pastoral society. This research describes a quantitative and qualitative study on the determinants of institutional delivery among pastoralists of Liben Zone with special emphasis on Filtu and Deka Suftu woredas of Somali Region, Ethiopia. The study was funded by the project "Fostering health care for refugees and pastoral communities in Somali Region, Ethiopia". This community-based cross-sectional study was conducted during November 2015. Interviews through a questionnaire and focus group discussions were used to collect the data. Proportional to size allocation followed by systematic sampling technique was used to identify the study units. The major determinants of institutional delivery in the study area were as follows: being apparently healthy, lack of knowledge, long waiting time, poor quality services, cultural beliefs, religious misconception, partner decision, and long travel. Around one-third (133, 34.5%) of the women had visited at least once for their pregnancy. More than half (78, 58.6%) of the women had visited health facilities due to health problems and only 27 (19.9%) women had attended the recommended four antenatal care visits. Majority (268, 69.6%) of the pregnant women preferred to give birth at home. Women who attended antenatal care were two times more likely to deliver at health facilities (AOR, 95% confidence interval [CI] =2.38, 1.065-4.96). Women whose family members preferred health facilities had 14 times more probability to give birth in health institutions (AOR, 95% CI =13.79, 5.28-35.8). Women living in proximity to a health facility were 13 times more likely to give birth at health facilities than women living far away (AOR, 95% CI =13.37, 5.9-29.85). Nomadic way of life, service inaccessibility, and sociodemographic and cultural obstacles have an effect on the utilization of delivery services. Increasing access, information, education, and communication need to reach pastoral women in need.