The radial variation in cell morphology of ten-year-old Melia azedarach trees planted in northern Vietnam was experimentally investigated. The earlywood fiber lumen diameter and latewood fiber lumen diameter were almost unchanged from pith to 6th ring before significantly decreasing and remaining constant from 7th ring outwards. In contrast, fiber cell wall thickness in both earlywood and latewood increased from pith to 7th ring before becoming stable towards the bark. The maturation age of earlywood vessel lumen diameter estimated by segmented regression analysis indicated that wood of the Melia azedarach could be classified into core wood and outer wood, and the boundary between core and outer wood may be located at 7th ring from pith. This should be taken into account in wood processing using M. azedarach grown in northern Vietnam.