Background. Trichomonas vaginalis is a sexually transmitted parasitic protozoan known to be responsible for an estimated 180 million new infections per year, making it the most prevalent nonviral sexually transmitted pathogen worldwide. Method. A crosssectional study design was conducted on vaginal swabs by wet mount and Modified Columbia Agar culture technique in Jimma University Specialized Hospital (JUSH), ANC clinic, Jimma, Ethiopia. The study was done to assess the magnitude and associated risk factors of T. vaginalis infection from December to May, 2011/2012. Result. A total of 361 pregnant women were involved in this study. From these, 18 (4.98%) of the pregnant women were positive for T. vaginalis infection by Modified Columbian Agar culture technique. Education status (AOR = 0.186, 95% CI: 0.059-0.585, < 0.05), patients with dysuria (AOR = 0.180; 95% CI: 0.046-0.704, < 0.05) and dyspareunia (AOR = 0.152; 95% CI: 0.035-0.667, < 0.05) were significantly associated with T. vaginalis infection. Conclusion. The prevalence of T. vaginalis infection at 4.89% is relatively high among young reproductive aged women. Because this infection increases the risk of HIV transmission and is associated with adverse pregnancy outcomes, there is a need for increased provision of health information concerning T. vaginalis to the community, educating women, screening, and treatment of T. vaginalis infection in Ethiopia.