Swine ascariasis is one of the major parasitic diseases to cause economic losses. This study was carried out to investigate the prevalence of Ascaris suum from slaughtered pigs and return the result to the farm (Feed - back). A total of 8,121 pigs (315 farms) were examined from January to November in 2007. The prevalence of farms detected with milk-spots was 42.9% (135 / 315 farms), and that of pigs with milk-spots was 7% (565 / 8,121 heads). Among 565 pigs with milk-spots, the pigs with grade 1 and grade 2 were 380 and 185, respectively. The percentage of pigs and farms detected with adult worm were 0.6% (45/8,121) and 7.3% (23/315) respectively. There was no statistical difference in affection rateamong seasons. The rate was 5.0% in spring, 8.8% in summer, 8.2% in autumn and 6.3% in winter. There was no enough difference in pig infection rate based on piggery type. The prevalence of milk-spots in stolic type and in sawdust one were 15% and 18.5%, respectively.