Oriental spruce is a very important commercial timber species in Turkey. Its distribution area is recognized as one of the 25 biodiversity hotspots in the world. The present study aims to model site index (SI) of oriental spruce stands using some topographic, climatic and edaphic variables in a mountainous ecoregion of the Eastern Black Sea, Turkey. Within this scope, 60 sample plots were visited in the study area, and the height, diameter at breast height and age of sample trees were measured. A soil pit was also dug in each sample plot for analyzing soil properties. Then, some physical (sand, silt, clay, plant available water capacity) and chemical properties (pH, electrical conductivity, organic matter content and exchangeable cations) were examined on each soil sample. Finally, regression tree and multiple linear regression methods were used to model SI. Their adjusted coefficient of determination (R-adj(2)) values were found to be as 0.70 and 0.53, respectively. According to the outperformed model, longitude, soil K+ content and landform were the most important factors affecting the SI. The results show that the regression tree model which is proposed in the present study may be used by forest planners and silviculture experts as a decision support tool for scheduling proper forestry activities.