Background: The World Health Organization recommends that a woman without complications should have at least four antenatal care visits, the first of which should take place during the first trimester (not > 16 weeks). But a high proportion of pregnant women in most developing countries attended the first antenatal care at a late time. In Ethiopia, the magnitude of late antenatal care follow-up initiation is 64%, and in the study area, it is 68.7%. However, the determinants of the problem were not identified, particularly in the study area. Objective: To identify determinants of late antenatal care initiation among pregnant women attending antenatal care in public health centers in Jimma Town, South West Ethiopia, 2021. Methods: A facility-based unmatched case control study was conducted from May 1–30. The cases (n = 177) were mothers who attended their first antenatal care visit at >= 16 weeks of gestational age, and the controls (n = 177) were mothers who attended their first antenatal care visit at <16 weeks of gestational age during the data collection period. Data was collected through face-to-face interviews using a pre-tested, structured questionnaire. Descriptive and summary statistics were done. Bivariate and multivariable logistic regression analysis was done using SPSS version 21.0 to identify candidate variables at P-value <0.25 and determinants of late antenatal care initiation at P-value <0.05, respectively. Results: The current study identified that age > 25 years (AOR = 2.623, 95% CI 1.059– 6.496), poor knowledge about antenatal care (AOR = 3.856, 95% CI 1.266–11.750), lack of history of abortion (AOR = 3.326, 95% CI 1.082–10.224), place of previous delivery (AOR = 3.926, 95% CI 1.023–15.063), recognizing pregnancy through missed periods (AOR = 3.631, 95% CI 1.520–8.674), pregnancy-related pain (AOR = 3.499, 95% CI 1.423–8.603), and lack of family support (AOR = 2.647, 95% CI 1.092–6.415) were determinants of late antenatal care initiation. Conclusion: Age > 25 years, poor knowledge about antenatal care, lack of history of abortion, place of previous delivery, recognizing pregnancy through missed period, pregnancy related pain, and lack of family support during antenatal care booking were determinants of late antenatal care initiation. Health facilities and respective health care providers should provide health education at the facility level regularly, with due attention to late antenatal care initiation