Abstract: The aim of this study is to show the effectiveness of prohibited operating zone. Generation scheduling is a crucial challenge in power systems especially under new environment of liberalization of electricity industry. This study is focused on the economical aspect of unit commitment problem. Since, the generating units may have certain ranges where operation is restricted based upon physical limitations of machine components or instability. Therefore, Prohibited Operating Zones (POZ) as a redundant constraint is considered, while the next load demand as a very important issue is deliberated. In this study generation scheduling of each hour is conducted by considering the next load demands to increase reliability of scheduling. The impact of hot/cold start-up cost is taken in to account in order to get an efficient generation scheduling via genetic algorithm. Case studies and numerical analysis presents significant outcomes, while it demonstrates the effectiveness and robustness of the proposed method.