The purpose of the present research was to investigate the interactions between tree layer diversity and some morphological traits and nutrient elements of hornbeam leaves in forests of Asalam, Guilan. Nine research plots (50m×50m) are sampled as a gradient from pure hornbeam stands to mixed stands with up to 9 deciduous tree species. Tree layer diversity and richness indices were measured and also leaves of hornbeam (Carpinus betulus L.) trees were sampled in overstorey within each plot. The results showed that there was no significant correlation between tree-layer richness and diversity values and leaf traits including leaf lenght, petiole lenght, veins distance, leaf thickness, leaf area and serration number. But, Regression analysis showed that tree-layer diversity and richness measures were significantly negatively correlated with leaf width, fresh and dry weight of leaves. Correlation coefficients indicated that basal area of hornbeam trees was significantly positively correlated with weight of dry leaves and and negatively with special area of leaves. The result revealed that there was significant positive correlation between tree diversity and Mn amount and ADF, but tree richness had significantly positively correlated with ADF.