During the biomass combustion, large amounts of ash which should be disposed of and utilized in an environmentally acceptable way are produced. Due to its chemical and physical composition, biomass ash has great potential for use as a soil amendment. Therefore, the aim of this study is to determine the effect of application of different doses of ash (0, 2 and 5 t/ha) on soil reaction (pH), soil plant-accessible phosphorus (P2O5) and potassium (K2O) content, humus content, total carbonates (CaCO3) and total nitrogen (N) under the perennial energy culture Miscanthus x gigantheus. The research was conducted at the experimental station "Šašinovec" of the University of Zagreb Faculty of Agriculture during 2020. The study showed that the application of ash after one year did not have a significant impact on soil reaction, humus content and total nitrogen content in the soil, but did significantly affect the content of carbonates, plant-accessible phosphorus and potassium. The content of carbonates decreased significantly during the observed period, and the application of ash (2 and 5 t/ha) resulted in significantly lower carbonate removal compared to untreated soil. The content of plant-accessible phosphorus also decreased significantly, and the application of ash (2 and 5 t/ha) contributed to its reduction. The content of plant-accessible potassium in the soil increased significantly during the observed period, which increased proportionally with the increase of applied ash doses. In the studied agroecological conditions, the application of ash had a positive effect on total carbonates and plant-accessible potassium, a negative impact on plant-accessible phosphorus content and had no significant effect on soil reaction, humus and total nitrogen content in soil under energy culture Miscanthus x gigantheus.