This study was conducted to determine some important factors of site selection for Esfahan 4th new town-Iran, with quantification of importance index for each factor and the effect of selected criteria in determination of the prioritized location for urban development. The study followed an explanatory analytical method based on field studies, analytical hierarchy process and technique for order preference by similarity to ideal solution model. This means that after defining the criteria and the significant parameters using Delphi technique and filling out the questionnaires by experts in environmental sciences and urban constructions, the rate of effectiveness of each factor and also the significant criteria in site priority and environmental decision making for new towns were determined by analytical hierarchy process model and “Expert choice” software. The results revealed that among the main defined criteria (i.e. physical, biological, economical-social, political and pollution dispersion) and sub-criteria selected by the experts for location of Esfahan 4th new town, the physical criteria with a weight of 0.453 designated nearly 45 % of the importance index to itself, standing at the first priority. Accordingly, the economical-social and pollution dispersion criteria were ranked at the second and the third place with weights of 0.307 and 0.116, respectively. The technique for order preference by similarity to ideal solution model, which is one of the methods for multi-criteria decision making, was then used to determine the best location scenario. Comparing the three proposed locations, alternative 1 was found to be more suitable as it was well-fitted to the defined criteria.