INTRODUCTION: Even though the World Health Organization recommends daily oral iron with folic acid (IFA) supplementation as part of the antenatal care to prevent anemia, still the utilization remains low in Sub-Saharan Africa, particularly in Ethiopia. Therefore, the aim of this study was to assess the magnitude of adherence of iron with folic acid supplementation and associated factors among pregnant women who were attending antenatal care (ANC). METHODS: A facility-based cross-sectional study was conducted from February 24 to March 23, 2020. Four hundred and twenty-two participants were selected using systematic random sampling technique. Data were collected using a structured questionnaire through face-to-face interview. Data were entered and analyzed using EpiData and SPSS version 20.0, respectively. Bivariate and multivariable logistic regression analyses were done to identify associated factors of adherence, and P<0.05 was used as cutoff to determine statistical significance at multivariable logistics regressions. RESULTS: In this study, 414 (98%) pregnant women participated. The mean age of the respondents was 28.69 ±SD 5.49 years. The magnitude of adherence of IFA supplementation among pregnant women was 67.6% (95%CI: 63.3-72.5). Pregnant women who had a past history of preterm delivery (AOR=3.70; 95%CI: 1.46-9.37), counseling on IFA supplementation (AOR=2.28; 95%CI: 1.15-4.53), high perceived benefit (AOR=2.72; 95%CI: 1.25-5.90) and high self-efficacy (AOR=2.91; 95%CI: 1.40-6.04) were found to be significant associated factors of adherence to IFA supplementation. CONCLUSION: In this study, adherence to IFA supplementation among pregnant women is relatively high. Past history of preterm delivery, counseling on IFA supplementation, perceived benefit and self-efficiency had association with adherence to IFA supplementation. Proper counseling and health education should be given to pregnant women to increase their adherence.