Ruminant’s diet in particularly consists of plants or their by product and waste product from agriculture. Mostly, this material contains high undegradable fiber such as cellulose, hemi cellulose and lignin. Plants cell wall comprises on average 23% lignin, 40% cellulose and 23% hemicellulose on dry matter basis (Coughlan and Hazlewood, 1993). Ruminant may use fiber as energy source in their diet. Degradation of fiber in ruminant takes place by rumen microbes. In contrast, the simple stomach can not use the fiber as energy source because they do not have rumen (pre gastric fermentation sac) and do not have endogenous enzyme that are capable to digest fiber, the digestibility achieved only by chemical and mechanical (acid in the stomach in pigs and grit in chickens) means. In rumen, anaerobic bacteria, protozoa and fungi have their role in fiber degradation. Mostly, the bacteria appear to be the dominant fiber digesting group. Digestibility of plants substrate depends on the season, harvest and phenolic component (Benner and Akin, 1988). The limiting factor of fiber digestibility in ruminant is presence of lignin, which make cellulose and hemicellulose unavailable by combining with them. The role and importance of lignin will be discussed in detail in the review.