This paper describes an initial analysis to evaluate the effects of a new vehicle emission standard "Decree of The State Minister of Environment of Republic Indonesia No 141 Year 2003" on the ambient air quality in Jakarta City. The decree is enacted to reduce emission loads from mobile sources. This new emission standard will be applied step by step: to new type/new model that launched in 2005 from January 2005, to four-stroke motor cycle (current model that still produced since several years before) from July 2006 and to all models from January 2007. Current and future emission loads are estimated with respect to major roads in the center of Jakarta city. It is found that in the long term, implementation of the new vehicle emission standard will significantly reduce emission loads from gasoline-type vehicles. However, the new standard seems not effective to diesel-type vehicles.