Background Toxoplasmosis is a common parasitic infection with high prevalence and worldwide distribution. It may cause severe disease in the fetus of newly infected pregnant women. Objective This study aimed to evaluate the seroprevalence of toxoplasmosis and its related risk factors among pregnant women in Ramsar city, Mazandaran province, north of Iran, from October 2017 to March 2018. Methods In this analytical-cross sectional study, specific anti-Toxoplasma gondii IgG and IgM antibodies were measured in 191 pregnant women by ELISA method. The length of T. gondii infection was estimated by the IgG avidity test. Demographic and behavioral information about pregnant women and possible risk factors of toxoplasmosis were collected through interviews. Results Specific IgG antibody against T. gondii was detected in 46.1% and IgM in 5.8% and both IgG and IgM antibodies were detected in 4.7% of pregnant women. The IgG avidity test did not show any acute case of toxoplasmosis. None of the demographic characteristics, such as age, occupation, place of residence, education, income, trimester of pregnancy, frequency of pregnancy, and history of abortion was correlated with toxoplasmosis. Moreover, behavioral characteristics, such as the source of consumed water, contact with soil, presence of cats in the household, consumption of vegetables, type of meat consumed, and the way of cooking meat had no significant correlation with toxoplasmosis seropositivity. Conclusion More than half of the pregnant women (54%) were toxoplasmosis-free and therefore at risk of acquiring this infection. Increasing the knowledge of pregnant women about toxoplasmosis prevention may reduce the risk of this infection during pregnancy.