Distiller's dried grains with solubles (DDGS) is a low-value co-product from dry grind ethanol production. Due to its high fiber content, DDGS is used primarily as a feed for ruminant animals. Conversion of the carbohydrate components in DDGS to biofuel would improve the overall economics of dry grind ethanol production. The effect of solid loading on pretreatment of DDGS and on subsequent acetone-butanol-ethanol (ABE) fermentation was examined. DDGS samples were subjected to pretreatments in six catalytic solutions, at three solid loadings (20%, 30% and 40% w/w). After a 72-h hydrolysis, experiments were conducted to examine the fermentability of the hydrolysates using Clostridium acetobutylicum P260. The solid loading in a pretreatment appeared to affect both the sugar yields obtained from enzymatic hydrolysis and the ABE fermentation of DDGS hydrolysates. The hydrolysate from alkaline electrolyzed water pretreatment at 30% (w/w) solids was found to be most favorable to ABE production, while that from sulfuric acid pretreatment was the least fermentable, although it produced the highest sugar yield.