During recent years, supplier selection process in the supply chain has become a key strategic consideration. Increasing worldwide awareness of environmental protection and the corresponding raise in legislation and regulations, green purchasing has become an important issue for companies to gain environmental sustainability. This paper presents an interesting idea, proposing a multi-product model to solve the multiple sourcing green suppliers' problems. The goal of our model is minimizing the costs due to environmental pollutions, purchasing and transportation. Time window constraints which are assumed in this paper have lots of real world applications. However, in supply selection problems, it is given little importance. Thus, for on time delivery to customers, we use this constraint in our mathematical model. In this study, a nonlinear mixed integer programming model (MINLP) provided and has been resolved using by software GAMS. Finally, a numerical example is presented and its results are analyzed latter.
