Objective: To determine the seroprevalence of Toxoplasma gondii (T. gondii) infection in dogs and cats in Zhenjiang City, Jiangsu Province, Eastern China, and to evaluate the main associated risk factors relating to exposure to T. gondii in this region. Methods: Sera from 160 dogs and 116 cats from Zhenjiang City were tested for anti-T. gondii antibodies using ELISA. The seropositivity by area of activity, sex and age was analyzed. Results: Overall, 21 dogs (13.1%) and 24 cats (20.7%) had antibodies to T. gondii. The infection rate in stray dogs (38.7%) and cats (28.6%) was significantly higher (P<0.05) than in household dogs (6.9%) and cats (18.2%). The seroprevalence in male dogs (14.8%) and cats (21.05%) were slightly higher than their female counterparts (11.4% in dogs and 20.0% in cats), but were not significantly differenent (P>0.05). A high proportion of dogs at 3 to 6 years of age were positive to T. gondii (20.0%) while cats with relatively high seropositivity rates were at 0 to 1 year of age (33.3%). Conclusions: The prevalence of T. gondii infection in dogs and cats in Zhenjiang City was high, which is probably the main source of T. gondii infection in this area.