The acid-soluble lignin determination used in analyses of lignin by the sulfuric acid method was evaluated. The conventional UV spectrophotometric method using the absorption at 205 nm is appropriate for hardwoods, whereas for softwoods and bamboo the absorption at 205 nm should be corrected, since the absorption maximum is shifted to a shorter wavelength in sulfuric acid solution. Therefore, in the latter cases, the actual absorption maximum should be used.