Two experiments were conducted to determine the optimum particle size of corn for growth performance, nutrient digestibility in pigs and cost effectiveness for the fine grinding. In Exp. 1, 72 nursery pigs(Duroc × Yorkshire × Landrace, average initial body weight 12.36±0.59㎏) were blocked by initial weight with weight and with six pigs per pen and six pens per treatment. The corn was ground in a hammermill through either screen opening of 3㎜(fine particle) or 4.5㎜(coarse particle). For 28 d, pigs fed fine corn diet were higher(P$lt;0.05) in average daily gain(ADG) than those fed coarse one, whereas no significant difference in average daily feed intake(ADFI) was found between the dietary treatments. Gain/feed and DM and N digestibility of pigs fed the fine corn diet were significantly improved compared to those of pigs fed the coarse corn diet(P$lt;0.05). In Exp. 2, a total of 48 finishing pigs(Duroc × Yorkshire × Landrace, average initial body weight 47.54±0.69㎏) were used in a 28 d growth assay. The corn was ground in a hammermill through either screen opening of 3㎜(fine particle) or 6㎜(coarse particle). During the experimental period, ADG, ADFI and G/F were not significant different between the treatments(P$gt;0.05). DM and N digestibility and intake of digestible nutrients were greater for pigs fed the fine corn diet than those fed the coarse one(P$lt;0.05). Also, pigs fed the fine corn diet had decreased fecal nutrient excretion compared to those fed the coarse com diet(P$lt;0.05). Total feed cost per ㎏ of weight gain was higher(921 vs 84l won) in the coarse group than in the fine one. In conclusion. fine particle size of com resulted in greater growth performance and nutrient digestibility than coarse particle size of corn in nursery and finishing pigs.