Swine play an important role in the disease ecology of influenza. Swine may provide the potential for mixed infections and genetic reassortment between avian, human, and porcine influenza viruses. We investigated the prevalence of antibodies to swine H1 and H3 influenza viruses and avian H5 and H9 influenza viruses in feral swine in southern China. Serum samples were collected from 31 feral swine harvested in 2009 in southern China. Of 31 serum samples tested, 14 (45%) had detectable antibody to H1 influenza virus and 23 (74%) were positive for H3 subtype. The antibody prevalence against both the swine H1 virus and the swine H3 virus was 45% (14/31). Five samples were reactive with both H1 and N1 subtype viruses, suggesting exposure to H1N1 viruses. All the sera tested were negative for avian H5 and H9 influenza viruses. Further investigations of influenza virus exposure of feral swine are needed to clarify their role in influenza ecology.