ABSTRACT; Europe has already established tentative critical levels of air pollutants based on the dose responses, however, not yet in the Asia. The critical levels are becoming needed for evaluating plant responses to air pollutants in the East Asia. Current ozone level has the potential adverse impact to plants. On the other hand, Forestry Agency in Japan carried out forest health monitoring survey. However, the relation with air pollutants is not clarified. This study analyzed observation data by using GIS to evaluate the relationship between air pollutants and decline, quantitatively and visually. Study areas are Sugi (Cryptomeria japonica D. Don) forests in the Kanto plains, where many surveys and reports have been done. Geostatistical analysis (kriging method) was applied for making oxidant based AOT40 (Ox) map in the forest monitoring period of Forestry Agency. The distribution and range of AOT40 (Ox) were compared with daytime and nighttime, and different monitoring period. Furthermore, AOT40 (0x) values were extracted and analyzed at each monitoring point, to examine the relationship between the mean decline index and climate normals (ATP, Precipitation index) or land use (e. g. forest rate).