Swine influenza is an acute respiratory disease prevalent in pig-growing areas worldwide. In total, 518 gilt and sow serum samples and 14 litters (66 samples) of aborted fetuses from 37 farms (average of 14 serum samples per farm) in Gyeongbuk Province were collected between September 2010 and May 2011. All samples were examined for antibodies to swine influenza virus (SIV) H1N1 and H3N2 using enzyme-linked immunosorbent assay (ELISA). The seropositive rates of gilt and sows were 59.8% (310/518) for SIV H1N1, 78.8% (408/518) for H3N2, and 55.6% (288/518) for both subtypes tested. The rate of aborted fetuses was 13.6% (9/66) for H1N1, 9.1% (6/66) for H3N2, and 9.1% for both subtypes. The seroprevalence for H1N1 in gilts and sows was 46.6% (69/148) and 65.1% (241/370), respectively, and that for H3N2 was 78.4% (116/148) and 78.9% (292/370), respectively.