A simplified steady-state mass balance model for estimating critical loads was applied to a test area in Japan to evaluate its applicability. Three criteria for acidification limits were used. Mean values and spatial distribution patterns of critical load values calculated by these criteria differed greatly. To evaluate the uncertainty of the base cation weathering rate used for calculating critical loads, ion content and particle size distribution were measured for the soils collected from the test area. The base cation weathering rate was estimated with the PROFILE model based on these measurements. The base cation weathering rates estimated from surface geology were adequate as mean values, but had uncertainties of 50% of the averages.