High sulfur concentrations lead to soil acidification and, indirectly, to the mobilization of phytotoxic compounds, including aluminum and selected trace elements. On the other hand, sulfur deficiency decreases crop yield and quality. Previous studies investigating the effect of sulfur on the available potassium content of soil delivered inconclusive results. The aim of this study has been to determine the effect of increasing doses of sulfate sulfur and elementary sulfur on the content of total sulfur, sulfate sulfur and available potassium in soil samples collected at a depth of 0-40 and 40-80 cm. A three-year field experiment was conducted on acid brown soil of the grain size distribution of heavy loamy sand. The soil was acidic in reaction (pH1 M KCl dm–3 of 5.30) and contained the following concentrations of mineral nutrients: mineral nitrogen – 24.0, sulfate sulfur – 4.10, available phosphorus – 34.5, available potassium – 110.0 mg kg–1 soil. Three sulfate sulfur (S-SO4) and elementary sulfur (S-S0) fertilization levels were applied each year: S1 – 40, S2 – 80 and S3 – 120 kg ha–1. In most cases, NPK+S fertilization, in particular the application of 120 kg S ha–1, contributed to an increase in total sulfur concentrations in both sampled soil horizons compared with the NPK treatment. Sulfate accumulation in the soil increased over time, proportionally to the increasing rates of sulfur fertilizers. The effect of elementary sulfur application on an increase in the S-SO4 content of the 0-40 cm soil layer was noted in the third year of the study. During the three-year experimental period, the application of both sulfur forms decreased the available potassium content of soil samples collected at the depth of 0-40 cm in comparison with the NPK treatment. The available potassium content of the 40-80 cm soil layer varied after sulfur fertilization. Sulfate sulfur exerted a stronger effect than elementary sulfur on available potassium levels in the soil.