Septate wood fibers were abundant in the following parts of growth rings of Kalopanax pictus Nakai: 1) around the vessels, 2) in the vicinity of ray cells, 3) in terminal regions of the growth rings. Septum formation in wood fibers progressed from the initial region (pore zone) towards the terminal region within a current growth ring with progressing 1ignification of the wood fiber walls. Many septate wood fibers at the end of the growth ring had radially continuous septa. Karyokinesis was observed in severa1 wood fibers before the initiation of septum formation, while lignification was in progress after the completion of the S3 layer deposition. This suggests that the septation starts in parallel with the progress of lignification after the deposition of the S3 layer.