In order to study the degree of improved air quality as an outcome of the action plan of Atmospheric Environment Improvement in Gimhae, Gyeongnam Province, we investigated the status and trends of air pollutant before and after the plan. Nitrogen dioxide and ozone, both classified as hazardous substances, were closely monitored with particular attention. The level of sulfur dioxide, nitrogen dioxide, fine particles and ozone (but for carbon monoxide) was decreased after the plan was implemented. The number of days on which ozone exceeded the National Ambient Air Quality Standard has decreased, but the level was still often exceeded. The level of nitrogen dioxide did not surpass until the 2006 standard, but when the revised 2007 standard was implemented, it exceeded 80% of some standards. The yearly level of ozone has decreased since the plan was introduced. The concentration of nitrogen dioxide, however, has reduced in high order area while increased in low order area.