The experimental plots used in the study were located in the middle forest zone (elevation: 900-950 m a.s.l.) on two nappes of the flysch Carpathians in southern Poland. The aim of this study was to assess the effects of serpentinite in combination with nitrogen, phosphorus, and potassium fertilizers on selected chemical properties of the soil and activity of dehydrogenase and urease in the studied soils. All fertilizer treatments significantly enriched the tested soils in magnesium. The use of serpentinite as a fertilizer reduced the molar ratio of exchangeable calcium to magnesium, which facilitated the uptake of magnesium by tree roots due to competition between calcium and magnesium. After one year of fertilization on the Wisła experimental plot, the pH of the Ofh horizon increased, while the pH of the mineral horizons significantly decreased. Enrichment of serpentinite with nitrogen, phosphorus, and potassium fertilizers stimulated the dehydrogenase activity in the studied organic horizon. The lack of a negative effect of the serpentinite fertilizer on enzyme activity in the spruce stand soil showed that the concentrations of the heavy metals added to the soil were not high enough to be toxic and indicated the feasibility of using this fertilizer in forestry.