The aim of this study was to test if further grinding of corn DDGS is advantageous in terms of apparent total tract digestibility (ATTD) of DM, GE, nitrogen (N), and NDF in growing and finishing pigs. It was also tested to determine if ATTD was different between hammermill and roller mill grinding methods. There were 3 diets. Each diet consisted of 51% corn ground at 500 microns with a roller mill, and 45% of corn DDGS ground at 450 microns using a hammermill, or 45% corn DDGS ground at 450 microns using a roller mill, or 45% of corn DDGS not further ground (unprocessed) at 650 microns. Results show that particle size reduction either with a roller mill or a hammermill (from 650 to 450 microns) increased ATTD of GE and DM of corn DDGS, tended to increase ATTD of N, but had no effect on ATTD of NDF. Finishing pigs had grater ATTD of GE and CP than growing pigs (tended to be greater for ATTD of DM). There were no effects of growth stage in ATTD of NDF. There were no interactions between particle size reduction and growth stage. In conclusion, reduction of particle size of corn DDGS (650 to 450 microns) either with a roller or with a hammermill has a beneficial effect on digestibility of valuable dietary components in growing and finishing pigs.