Milled Bamboo Lignin (MBL) fromPhyllostachys pubescens (Bambuseae)was found to containp-hydroxycinnamic acid (PC), guaiacylpropane and syringylpropane units in an approximate molar ratio of 1:4:3 on the basis of chemical and spectroscopic analyses. In addition, the MBL is comprised of a guaiacylsyringyl type lignin-core and PC type peripheral groups. At least 9 PC type units/100 C9-units were chemically bonded to the lignincore in the form of ester linkages at C-a and C-γ, and the remainder in the form of aryl ether linkages at C-a. Bamboo kraft lignin (BKL) was found to be a lignin of the guaiacyl-syringyl type, having a higher degree of condensation and a higher phenolic hydroxyl content than the MBL. The major low-molecular-weight constituents of bamboo kraft black liquor were determined to be acetosyringone, syringic acid, acetoguaiacone and vanillic acid. Structural change in bamboo lignin during kraft cooking are discussed on the basis of the observed results.