Abstract: Chemical compositions,fiber characteristics and pulping properties of Broussonetia papyrifera bark at different ages were researched in hot-valley of Jinsha River.The results showed that the paper mulberry bark has the characteristics of long-fiber,lower lignin content,higher holocellulose and well fiber shapes and is suitable for pulping.With the growing of trees,the chemical compositions of the lower aged bast increase slightly.But to 6—7 years trees,the pulping process are hampered for the glucose and lignin increased obviously while fiber and HNO3-C2H5OH content decreased sharply.1% NaOH extractives increased gradually and came up to the maximum when the tree was 6—7 years old.The fiber length,ratio of fiber length to width and fiber proportion increased with the growing of trees,coming up to the maximum when the tree was 3—5 years old,then declined obviously at the 6th year.2—4 years old trees have better strength and folding endurance and became stable at 5th—7th years.As a result,the ideal material of the high-quality fiber comes from 2—5 years old trees.Based on economic efficiency,2—3 years fiber material plantation rotation is proposed.