The present methods of opal phytolith analysis still limits an accurate reconstruction of past environment. In this paper opal phytolith assemblage and its relation with plant biomass was studied. Opal phytolith production of some common grass and tree species was determined mixing leaf blades at different ratios. All plants showed some variability in the production of opal phytoliths, especially for those from Bulliform cells (Fan shape). The results showed that leaf blades of Sasa kurilensis produce about 23 times more Fan shape phytoliths and 27 times more Bambusoid phytoliths than the quantity of Jigsaw-puzzle opal phytoliths produced by Fagus crenata leaves. Generally, to have similar amounts of tree and grass origin opal phytoliths in soils, the quantity of tree leaves should be more than 10 times of that of the grasses. The clear results obtained for the plant species studied show that the determination of opal phytolith ratios between species is a good tool to estimate plant biomass and consequently to achieve a more precise reconstruction of past vegetation.