Background:Even though spontaneous abortion (SA) is an important public health concern, most studies in our country were confined to induced abortion. Thus, this study aimed to assess the prevalence and associated factors with SA among reproductive-age women in Benchi Maji, Kefa, and Sheka Zone, southwest Ethiopia.Methods:An institution-based cross-sectional study was conducted from April 1 to 21, 2021, among 845 reproductive-age women in a public hospital that serves residents of Benchi Maji, Kefa, and Sheka Zones by using two stages simple random sampling technique. Data were collected by interviewer-administered semi-structured questionnaire entered into Epi-data version 4.2 and analyzed by SPSS version 23. Bivariate and multivariable logistic regression analyses were undertaken. The odds ratio at 95% confidence interval (CI) andp-value < 0.05 was used to ascertain statistical significance.Results:Nearly one-tenth (12.31%) of the participants had SA within five years preceding the survey. Being in between 15 and 19 years (AOR 0.102; 95% CI = 0.044–0.235) at (p-value < .001), being an urban resident (AOR 0.461; 95% CI = 0.255–0.833) at (p-value = .01), having education level primary or below (AOR 23.5; 95% CI = 6.3–88.3) at (p-value < .001), having middle income level (AOR 3.89; 95% CI = 1.88–8.08) at (p-value < .001), and being married (AOR 0.319; 95% CI = 0.186–0.548) at (p-value = .044) were factors associated with it.Conclusion:The prevalence of SA among the participants was within the worldwide average prevalence. Having planned pregnancies before 35 years, minimizing hard labor works, and other risks for SA are beneficial to reduce the prevalence of SA. Thus, health care providers should work on awareness creation toward preventable risks of SA among the study participants.