By determining the environmental factors affecting the plant species in a particular site, the presence of the species in the site can be predicted. The aim of this study was to investigate the response of Buxus to environmental variables individually and to extract its ecological optimum and amplitude in relation to the most important environmental factors using HOF function. This study has been done in the major sites of Buxus hyrcana in the Hyrcanian forests. 834 sample plots (400 m2) were established by systematic-selective method and within each plot, the presence of this species, topographic factors and some soil variables were recorded and measured. Fitting the response curve to the environmental variables with HOF function showed that pH, altitude, and clay were the most important variables on the performance of box tree. The results of this study showed that the response curves of Buxus species relative to the elevation and clay are unimodal and right-skewed, for sand variable is left- skewed, for nitrogen is symmetric and for the remaining variables are monotonically increasing or decreasing. The general conclusion based on the ecological optimum amount for each variable showed that the Buxus tree is lime- and moisture-demanding species, which is present in low altitudes, steep slopes and light soils with high nitrogen content. Since simultaneously more than one factor affects the behavior of species, it is recommended that the shape of the Buxus response curve is studied by taking into account the environmental variables in combination and by using other models.