This study describes radial variation in fibre length, vessel element length, vessel lumen diameter, and ray width (number of cells) in relation to the developmental stages in radial stem increment in Zelkova serrata trees. Maturation age (the age at which the size of the wood elements is stabilized) was compared to the ages at the boundary between the early and middle stages (age t1), and the middle and late stages (age t2) of radial stem increment. The maturation age was estimated by nonlinear segmented regression analysis. Ages t1 and t2 were estimated by the Gompertz growth function. The maturation age for the length of axial elements (wood fibres and vessel elements) was not related to either age t1 or age t2. However, the maturation ages for vessel lumen diameter and ray width were close, and both were related to age t2. This indicates that the maturation of vessel lumen diameter and ray width was synchronized and both were related to the stage of radial stem increment.