Chiba prefecture is located in the eastern side of Tokyo Metropolitan Area(TMA), and it is adjacent to the city of Tokyo. In this area, air pollution is a serious environmental issue, which is caused by the pollutants emitted within and around the area. In order to prevent air pollution, a new Air Pollution Monitoring and Management System was introduced by the Chiba prefectural government in April, 1996. This system consists of real-time ambient air quality and source monitoring, data processing system and an air quality forecasting system. Almost 130 air monitoring stations transmit hourly air quality and wind data to the system center. Sixty-five major industries also transmit hourly emission intensity and related source data. The advanced air quality forecasting system can predict future ambient levels of photochemical oxidant(Ox) and nitrogen dioxide(NO2) up to 48-hours based on the predicted meteorological conditions. Photochemical air pollution warnings are issued when the hourly values of Ox exceed 120ppb and the adverse meteorological conditions are predicted to sustain these levels. When air pollution forecasting warning is issued based on the results obtained from the forecasting system, the emergency information are sent rapidly to the municipalities and to operating factories in order to mitigate the effects of high air pollution.