Finding the best location is the first and most fundamental step in planning for offering a service or product to costumers. To locate appropriate location, scholars have suggested a  variety of models based on circumstances and conditions. Equality is of importance in locating models in the utility sector and in making equal accessibility to urban utilities for members of  the society; it has an effective role alongside other criteria  such as efficiency and effectiveness. Finding a proper location for retail chain supermarkets with equality as  the  main concern, would contribute to some factors  such as  reduction of  costs, feasibility of access, and equality in distribution. This research was conducted to find  the  best location for retail chain supermarkets so that each costumer has an equal distance to the nearest store. In this research, minimization of the Gini coefficient of the Lorenz curve based on service distance has been applied.  Based on Gini coefficient of the Lorenz curve function, an algorithm has been designed to find an  optimal location for a retail chain supermarket in a bounded flat  environment with defined population centers and demand.