Comparing with the previous Auto/Oil programs, the total plan and current status of the air quality modeling study in JCAP are presented.The total plan of air quality modeling study has the following characteristics: 1) Vehicle emission inventory program is developed by considering the original features of Japan. 2) Not only the urban air quality but also the road sides pollutants dispersion is evaluated. 3) The chemical reaction model for the secondary particulate formations is developed on the basis of the smog chamber experiments. 4) For the cost-effectiveness analysis of vehicle/fuel technologies, the output of the air quality modeling will be combined with the cost data of new vehicle emission reduction technologiesAs the first step, preliminary modeling studies are conducted to understand the overall tendency of the air quality change toward 2010 in Tokyo urban area.Following results are cleared. 1) UAM and CIT program have the potential to predict the urban air quality in Tokyo area. 2) Major Hydrocarbon source in Tokyo area is from the painting, the contribution from vehicles is less than 10 %. 3) For the NOx emission, around 35 to 40 % of the total emission is caused by vehicles, especially Diesel. 4) Reduction of NOx emission is effective for the improvement of ozone concentrations 4) Reduction of maximum ozone concentration less than 60 ppb seems to be very hard.Although these studies are based on the emission factors for current fuel/vehicle technologies, in the next step, more detailed studies including particulate formations and pollutants dispersion of road sides will be carried out in JCAP.