Seroprevalence of Toxoplasma gondii infection in fattening pigs in Heilongjiang Province, northeast China, was investigated between July 2011 and June 2012. In total, 1,014 pig serum samples were collected from 10 administrative regions and assayed for T. gondii antibodies by indirect hemagglutination (IHA) test using a commercially available kit. The average T. gondii antibody-positive prevalence was 4.6% (47/1,014), which is relatively lower than that in other provinces in China. Seroprevalence in fattening pigs raised on small farms (6.3%) was significantly higher than that on large farms (3.8%) (P < 0.05), and the seroprevalence ranged from 2.4% (Shuangyashan) to 6.8% (Qitaihe) between different geographical regions. Given that pork is not examined for T. gondii infection in China by law, these findings have public health implications and provide useful baseline information for the control of pig toxoplasmosis in this unique region of China.