Reports of dogs with H3N2 canine influenza virus (CIV) have been documented frequently. To better understand the seroprevalence of H3N2 CIV among dogs in northeast China, here we report for the first time a relatively high seroprevalence of H3N2 CIV infection in dogs in northeast China. Forty-five of the 223 canine sera (20.2%) and 166 of the 500 canine sera (33.2%) tested feral dogs and pet dogs were seropositive by NP-ELISA, which is higher than that in southern China. The relative data provided in this report can be useful for small animal practitioners or public health policy makers to carry out relative measures for the prevention of this disease. Meanwhile, similar seroprevalence studies and prospective natural history and incidence studies should also be undertaken in other places.