Abstract: The physical and mechanical properties of timber sampled from different aged trees of Betula alnoides were determined. The results showed that the density, shrinkage and major mechanical properties of the timber increased along with increment of the sampled tree ages. According to 't' test results that there were significant differences in the above properties of the wood between samples from 7 and 11 year old, and between 15 and 19 year old trees of Betula alnoides. There were significant differences in some of the indices determined among 11, 15 and 19 year old timber samples, whereas there were no significant differences in some other indices among the 3 groups of different aged trees. So, the effect of tree ages on wood properties must be considered carefully when Bethla alnoides wood is to be utilized.