Because of the need to keep balancing between electricity supply and demand continuously, a demand analysis is necessary as it can provide essential information to manage operation of a power system. This study presents a seasonal peak demand characteristics investigation for commercial area in Japan by developing hourly demand regression models for each season. Meteorological parameters and existing holidays are considered as demand drivers. Many standard statistical tests are applied to the models. From results, typical forms of link between commercial demand and key drivers at peak hours (daytime and evening) in each season can be revealed through the models. Knowing more detail characteristic of a demand particularly during high load hours can help utilities to maintain expected optimal operation of power systems and service to consumers all the time.