Maturation rate, the rate of increase in tracheid length in juvenile wood, was examined in sugi (Cryptomeria japonica D. Don) saplings grown for five years under different shading conditions: 10%, 20% 40% and 100 % of relative illumination intensity. The lowest photointensity dramatically suppressed radial growth and slowed tracheid lengthening. Radial variation of tracheid length within the stem was associated with distance from the pith, rather than the number of annual rings from the pith. Furthermore, maturation rate was closely related to the rate of the radial growth, which changed proportionally with growth rate below a 2-3 mm ring width. A lower maturation rate of tracheid length is associated with a delay in the transition from juvenile to mature wood.