Barley is a dominant feed grain in Iran, western North America, and Europe. Barley processing is imperative to maximize its utilisation by feedlot and dairy cattle (Yang et al, 2000). Whole grain with an intact pericarp is largely or entirely resistant to digestion by ruminants because whole kernels are resistant to bacterial attachment (Beauchemin et al, 1994) in the rumen. In addition to pericarp, barley grain is surrounded by a fibrous hull, which is of low digestibility. barley kernels are not severely damaged by chewing. Consequently, considerable whole barley kernels are excreted in feces if whole barley kernels are fed. So the objective of this study was to investigate effects of processing on ruminal degradability of barley and trend of ruminal digestion of ground barley in different sizes.