Acid deposition has caused tremendous stress to forest ecosystems. Increased soil acidification due to acidic inputs from acid deposition may cause declines in forest productivity through the depletions of soil nutrients, increased mobility of aluminum, and increases in acid anion concentrations, primarily nitrate and sulfate. The retention of sulfate in soil is a critical mechanism regulating soil acidification. Sulfate adsorption acts as a buffer delaying the elevation of solution sulfate concentrations. Sulfate adsorption capacities of forest soils in the Otter Creek Wilderness Area of the Monongahela National Forest were determined using the adsorption isotherm method. Several factors may influence sulfate adsorption such as the surface charge on soil particles, the presence of iron and aluminum oxides, the ionic strength and pH of the soil solution, and the competitive effects of nitrate. These factors were also accounted for experimentally. By determining the maximum amount of sulfate retention in the soil, and the factors that have the most influence on sulfate adsorption, we can evaluate the current effects of acid deposition on forest soil in this region and the susceptibility of these soils to nutrient depletion and further acidification.