From the wood-flours of pine four kinds of sample, different in lignin contents, were prepared by the sodium chlorite treatment. The samples thus obtaind were cooked by alkaline processes, and the brightness and the purity of color of cooked samples were examined. The results show that the brightness decreases first, then increases and finally decreases again, and that the purity increases first, then decreases, and finally increases again. The time at which the brightness of samples decreases again almost coincides with the time at which the purity of color of samples increases again.