The use of by-product in animal nutrition is necessity since it may increase the availability of feed for animal and avoid accumulation that contributes to environmental problems. Sugar cane bagasse and pith, by- product which leave the last processing stage of the sugar mill (bagasse) and passed through rotary sieves to separate fine particle (pith), are the most abundant by-product in Iran. The low digestibility, high lignin and very low content, are considered the main reasons for unsatisfactory performance of animals fed this roughage. Steam-pressure treatment cleavage the bounds between lignin and the other component of the cell wall, in order to improve it's degradability by enzymes of the rumen microbial ecosystem. The objective of this work was to evaluate the chemical composition and in situ degradability of sugar cane pith treated by steam at high pressures.