Grain sources and processing have been discussed for many years. Most feedlots select their grain source based on cost of the grain plus its processing. A variety of processing methods have been devised that vary in cost and effectiveness. The primary goal of processing is to increase energy (starch) availability. In addition, processing may destroy mycotoxins and improve mixing characteristics to improve bunk management and thereby enhance animal performance (Owens et al, 1997). Mechanical and chemical alterations during processing increase surface area exposure and improve ruminal, intestinal and total tract starch digestibility of seed grains (Huntington, 1997; Owens et al., 1997). Unprocessed corn can be effectively fed to ruminants because the pericarp of the kernel is extensively damaged by chewing (Beauchemin et al, 1993). So the objective of this study was to investigate effects of processing method and size of corn ground particles on ruminal degradation parameters.