Background – Sexually transmitted infections are defined by a variety of clinical syndromes caused by pathogens that can be acquired and transmitted from one person to another through unprotected sexual activity. In the developing world, sexually transmitted infections are widespread and can lead to profound impact on sexual and reproductive health including adverse pregnancy outcomes. Even in the presence of the adverse pregnancy outcomes, studies on the prevalence and associated factors of sexual transmitted infection among pregnant women in Ethiopia, especially in the study setting are limited. Objective – This study tried to assess prevalence and associated factors of sexually transmitted infections among pregnant women attending antenatal care In Public Hospitals, Addis Ababa, Ethiopia, 2022. Method: - Institution-based cross-sectional study was conducted among 302 pregnant women attending antenatal care in selected public Hospitals Addis Ababa, Ethiopia from August 1- September 1/2022. A systematic random sampling technique was used to select the study participants and data were collected using pretested structured face-to-face interview questionnaire with chart review. The data were entered using EP info version 7.2.2.2 statistical software and analyzed using Statistical Package of Social Science version 25. Descriptive statistics was used to describe the study population concerning relevant variables. Bivariate and multivariable logistic regression analysis was employed to estimate the crude and adjusted odds ratio with a confidence interval of 95% and P value of less than 0.05 considered statistically significant. Result: In this study the prevalence of sexually transmitted infections was 27.5% (95%CI 22.5%-33.1%). Having history of abortion (AOR= 3.59;95%CI:1.72 5.45), having history of still birth (AOR=2.41;95%CI:1.61,4.06), having multiple sexual partner (AOR= 3.97;95%CI: 1.99,5.95) and drinking alcohol (AOR= 2.09;95%CI:1.89,3.28) showed a significant association. Conclusion: The prevalence of sexually transmitted diseases in public hospitals of Addis Ababa is high. History of abortion, history of still birth, having multiple sexual partners and drinking alcohol showed a significant association. It is better to update the syndromic approach, encourage monogamous relationships and avoid risky sexual behaviors to reduce the burden of STIs. Key words: sexually transmitted infections, Addis Ababa, pregnancy. 1. INTRODUCTION