This study was carried out to determine the effects of different processing methods on in vitro rumen fermentation kinetics and gas production (GP) of corn grain in total mixed ration. To evaluate different processed corn grain used in a total mixed ration, an in vitro rumen GP technique was utilized. Treatments included were 1) corn grain (20%) in a total mixed ration (TMR), 2) steam flaked corn (SFC) 20% in TMR, 3) extruded corn (20%) in TMR, 4) corn grain (10%) + SFC (10%) in TMR, 5) Corn grain (10%) + Extruded corn (10%) in TMR, 6) SFC (10%) + extruded corn (10%) in TMR. The TMR included alfalfa hay (40%), beet sugar pulp (10%), soybean meal (10%), barley grain (20%) and 20 percent of corn grain (CG) which was replaced by processed corn to prepare the experimental treatments. There were significant differences (P<0.05) in gas production among treatments throughout the incubation times. There was a significant difference between treatments at 12 h (P<0.05) for total GP and treatment 2 produced the highest volume of gas and the treatments 1, 3, 4 and 5 produced the lowest volume. After 24 h of incubation of samples, same trend was recorded and treatment 2 produced highest (P<0.05) GP compared to other treatments. Potential GP (a+b) was highest (P<0.05) for treatment 2 with no significant differences with treatments 1, 5 and 6. Consistent with a+b and b fractions, the rate of GP “c” was affected by treatments (P<0.05). As a result, steam flaking of corn seems to have potential to increase starch fermentation in the rumen. It is possible to alter the site and extent of digestion of cereal grains to increase the digestibility of concentrate feeds.