The effect of soil acidification on the content of nitrogen active forms N-NH4 and N-NO3 in a soil sample was studied on the basis of laboratory experiment which included 4 different soils. Different pH values which occur in Polish soils (pH 3.5, 4.0, 5.0, 6.0, 7.0, 7.5) were simulated by the addition of particular volumes NaOH or HCl according to buffer capacity of the soil and 60% of field water capacity was maintained for 6 months. Extraction of NH4+ and NO3- was carried out with redistilled water after their incubation. Soil–water mixture was filtered under pressure and after that the content of nutrient active forms was measured in the received solution. It was found that differentiated pH of soil models influenced the content of nitrogen active forms.