Two experiments were conducted to determine the interactive effects of particle size reduction and pelleting on the apparent ileal digestibility (AID) of starch, standardized ileal digestibility (SID) of amino acids (AA), apparent total tract digestibility (ATTD) of fiber, fat, calcium, and phosphorus, and net energy (NE) in corn-soybean meal diets fed to pigs. Six corn-soybean meal based diets were arranged by 3 × 2 factorial with 3 particle sizes of corn (i.e., 700, 500, or 300 μm) and 2 diet forms (i.e., meal or pelleted). An N-free diet was also used in Exp. 1. Pigs were allowed ad libitum access to feed and water in Exp. 1 and 2. In Exp. 1, seven pigs (initial weight = 59.30 kg) that were equipped with a T-cannula in the distal ileum were allotted to the 7 diets using a 7 × 7 Latin square design with 7 periods. Ileal digesta were collected for 2 days after 5 days of adaptation. Results indicated that there were no interactions in the AID of starch and the SID of Arg, His, Ile, Trp, and total AA. The interactions were observed for the SID of Leu, Lys, Met, Phe, Thr, and Val (P < 0.05). Regardless of particle size, values for the AID of starch and the SID of most AA were greater (P < 0.05) in pelleted diets than in meal diets. Regardless of diet form, values for the AID of starch and the SID of most AA were linearly increased (P < 0.05) by reducing corn particle size. In Exp. 2, twenty-four pigs (initial weight = 29.52 kg) were allotted to the 6 diets using a 6 × 6 Latin square design with 6 chambers (i.e., 4 pigs/chamber) and 6 periods. Oxygen consumption and CO2 and CH4 productions were measured during fed and fasting states and fecal and urine samples were collected. Result indicated that no interactions were observed for the ATTD of P and total dietary fiber (TDF) and N retention. The interactions were observed for the ATTD of gross energy (GE), Ca, N, soluble dietary fiber (SDF), insoluble dietary fiber (IDF), and acid hydrolyzed ether extract (AEE) and concentration of NE (P < 0.05). Regardless of particle size of corn, the ATTD of GE, N, SDF, and AEE, and concentration of NE were greater (P < 0.05) and the ATTD of Ca and P was less (P < 0.05) in pelleted diets compared with meal diets. The ATTD of TDF and IDF and retention of N were not affected by diet form. Regardless of diet form, the ATTD of GE, N, SDF, and AEE and concentration of NE were linearly increased (P < 0.05) by reducing particle size of corn. There were no effects of reducing particle size of corn on the ATTD of Ca, P, IDF, and TDF and retention of N in meal or pelleted diets. In conclusion, the effects of reducing particle size of corn on the digestibility of starch and AA and NE were more pronounced if particle size of corn was reduced from 700 or 500 μm to 300 μm in meal diets and if particle of corn was reduced from 700 to 500 μm or 300 μm in pelleted diets.