Pipelines are essential for transporting energy resources over long distances. Pipeline projects cause many environmental, economic, and social problems. The construction of large-scale infrastructures such as natural gas/oil pipelines involves extensive disturbance for regional ecosystems. Therefore, it is very important to ensure bad effects of transmission pipeline routes considering environmental sensitivities. In order to do this, we used a geographical information system with multi-criteria decision-making techniques to create an environmental care model. In this study, we applied the order preference by similarity to ideal solution technique to integrate environmental sensitivity into the planning of a natural gas transmission pipeline project. For this purpose, route optimization was carried out for the ongoing operation of an existing 84.33 km natural gas transmission line. An environmentally sensitive optimum route was determined according to environmental impact assessment criteria. The experimental studies confirmed that our road is superior to the current road when compared with the 13 spatial criteria used for analysis. Our road has only seven stream passes while the current road has 20, our road has no quality soil pass on the other side while the current road has a 661-m quality soil pass, and our road is more cost-efficient at 77.89 km as opposed to the current road's 84.33 km.