Introduction: Contraceptive methods are techniques used to prevent pregnancy during sexual intercourse. The primary goal of contraception is to inhibit the fertilization of an egg by sperm or to prevent the implantation of a fertilized egg in the uterus. Unwanted pregnancy is a major challenge for street beggar women. Due to limited use of modern contraception, unwanted pregnancy and STDs are key issues faced by this population. This study aims to assess modern contraceptive utilization and explore factors influencing contraceptive choices among street beggar women in the Sidama region, Ethiopia by using Bayesian logistic approaches. Methods: A cross-sectional quantitative study was conducted on reproductive-aged (15–49) street beggar women in the Sidama Region. Data was collected using a pre-tested, structured interview questionnaire in the local language from each town in the Sidama region. Descriptive and inferential statistics were used to analyze the data using STATA version 17. A Bayesian logistic approach, with Markov Chain Monte Carlo methods, was used to model the association between modern contraceptive utilization and independent variables, allowing for estimation of model parameters and credible intervals. Result: The study found that 38.9% of street women in the Sidama region used modern contraceptives, primarily implants and injections. Bayesian logistic regression identified key factors influencing contraceptive use including, women aged 25–34 (AOR: 2.69 (95% CI: 1.57, 4.26)), married women (AOR: 4.91 (95% CI: 2.67, 8.51)), Widowed women (AOR: 2.81 (95% CI: 1.49)) and educated women (AOR: 2.16 (95% CI: 1.48, 3.01)) were more likely to use contraceptives. In contrast, those living on the street (AOR: 0.12 (95% CI: 0.05, 0.27)), with no history of pregnancy (AOR: 0.07 (95% CI: 0.02, 0.16)), and no sexual activity in the last six months (AOR: 0.11 (95% CI: 0.01, 0.03)), had lower usage rates. Additionally, women whose only job was begging (AOR: 0.43 (95% CI: 0.13, 0.92)) and those lacking health advice (AOR: 0.25 (95% CI: 0.07, 0.59)) also showed reduced utilization. Lack of discussion about contraceptives with partners (AOR: 0.18 (95% CI: 0.08, 0.33)) and no women's approval (AOR: 0.18 (95% CI: 0.08, 0.33)) further contributed to lower usage. Conversely, good knowledge of modern contraceptives was positively associated with utilization (AOR: 2.33 (95% CI: 1.44, 3.64)). Conclusion: The findings of this study identified several factors significantly associated with modern contraceptive use among street beggar women in the Sidama region, including age, marital status, Education level, disability, Job in addition to begging, Current living situation, history of sexual assault/rape, History of pregnancy after street life, discussion of modern contraception with a sexual partner, Advice from a health professional, Sexual activity in the last six months, time taken to arrive at a health facility on foot, approval of modern contraception, and knowledge. The main barriers reported were fear of side effects and lack of knowledge about contraceptive methods. The study suggests that concerned stakeholders should intervene to address these factors and improve modern contraceptive uptake in this vulnerable population. [ABSTRACT FROM AUTHOR]