The phenological characteristics and light dependence of the photosynthetic rate of Yachidamo ash (Fraxinus mandshurica var. japonica) were examined in view of the developmental difference between seedlings and saplings. The leaf-emergence duration and ‘leaf duration’ of seedlings were longer than those of saplings. The light compensation point at 20°C of photosynthesis was lower in seedlings than in saplings. The initial slope of the light-photosynthesis curve of seedlings was steeper than that of saplings. At higher light energy above 145 μE⋅m-2⋅s-1, the photosynthetic rate was higher in saplings than in seedlings. The light was saturated at 635 μE⋅m-2⋅s-1 with photosynthetic rate of 12.50 mgCO2⋅dm-2⋅hr-1 for the former, and at 355 μE⋅m-2⋅s-1 with the rate of 6.18 mgCO2⋅dm-2⋅hr-1 for the latter. Dark respiratory rate of a leaf was higher in saplings than in seedlings in the temperature range of 6°-30°C. The above mentioned results imply that the seedlings and saplings of Yachidamo ash seem to change their photosynthetic functions and phenological characteristics with its developmental stage under different habitat conditions.