This paper introduces the architecture and the deployment of a Cloud based decision support system (DSS). The DSS the authors proposed is deployed on a platform Cloud (CloudBees) and managed by the OpenStack infrastructure. The DSS is built on the Cloud Computing architecture with three layers and includes the multiple criteria decision making (MCDM) method PROMETHEE II as well as the procedure of negotiation Hare in order to help the decision makers to select the best urban project. The Cloud based DSS reduces the deployment and processing time, ameliorates the communication and the cooperation between the decision makers, facilitates the accessibility and decrease the cost. The Cloud based multiple criteria DSS the authors designed and implemented has significant advantages. It reduces the deployment and processing time, ameliorates the communication and the cooperation between the decision makers, facilitates the accessibility, and decrease the cost.