Objectives To assess the seroprevalence and associated risk factors of toxoplasmosis among HIV patients in Agaro Town Health Center of Jimma zone. Methods Convenient sampling was used to collect blood samples from 135 patients attending anti-retroviral therapy from February to March 2015. Serum samples were tested for anti-Toxoplasma gondii (T. gondii) antibody by using latex agglutination test. Structured questionnaire was used to collect data on socio-demographic and risk factors associated with toxoplasmosis. Results Overall seroprevalence of toxoplasmosis was 80.7% (109/135, CI: 74.04–87.36). In multivariate analysis significant association was observed between anti-T. gondii seropositivity and raw meat consumption (OR: 3.514, CI: 1.167–10.581, P = 0.025), knowledge about toxoplasmosis (OR: 5.225, CI: 1.382, P = 0.015) and sex (OR: 4.023, CI: 1.382–19.762, P = 0.015). Conclusions Immuno compromised patients showed high rate of seropositivity and thus, it is highly advisable to introduce routine anti-T. gondii antibodies serological screening test prior to ART commencement.