Forest roads are basic precondition for the sustainable management of forest resources. These roads entail a complex engineering effort because they can cause substantial environmental damage to forests and include a high-cost construction. Therefore, the design of forest road routes should have taken into account in terms of environmental impacts. In order to do this, the Geographical Information System (GIS) with Spatial Multi Criteria Decision Making (S-MCDM) techniques is a useful tool for creating a model. One such S-MCDM is the Spatial-integrated Technique for Order Preference by Similarity to Ideal Solution (S-TOPSIS). In this study, S-TOPSIS was applied to integrate environmental impacts into the design of a forest road route. Using the current forest road route (CFOR) and the GIS-based S-TOPSIS method, an environmentally sound forest road route (ESFOR) was determined according to environmental criteria. Five environmental criteria (avalanche, river, soil, geology and slope) were used for analysis to compare with. The results obtained from the analyses, are compared to the current forest road route. The CFOR 15.385 km in length, while the ESFOR found by S-TOPSIS was 14.385 km. If the differences in length between two roads multiplied by the width of the road (1km X 5m), the result would be 0.5 ha. The results showed that this methodology can provide environmentally sound road network also help to design quickly and less costly. These results suggest that spatial multi criteria decision making method can be more accurate in terms of environmentally sensitive forest road designing in mountainous area.