Introduction: Health Extension Program is implemented in Ethiopia since 2004 as a flagship of preventive, promotive, and basic curative services for poor and rural community, especially for children and mother. The purpose of this study is to examine the determinants and variations in health extension service utilization in Dera district, Oromia, Ethiopia. Methodology: Three-stage cluster sampling was used to select a random sample of 534 households from 10 kebeles of the district. The study used both descriptive and inferential statistics to identify the determinants of Health extension service utilization and variations. Result: The descriptive result revealed that out of 534 respondents, 223 (41.8%) of them utilized and 311 (58.2) of them not utilized health extension service given at the health post and outreach level. The random intercept binary logistic regression analysis identified that mother's age, mother educational level, mothers' employment status,