BACKGROUND: Red mud is increasingly considered a valuable by-product requiring development of new re-use technologies instead of deposition as waste. This paper reports the results of a microcosm study aiming to reveal the beneficial effects of the Ajka red mud, as soil ameliorant, on a specific acidic sandy soil in eastern Hungary. RESULTS: The red mud amount mixed into the sandy soil ranged between 0 and 50%. The experiment was monitored by an integrated methodology combining physical and chemical methods with biological and ecotoxicological measurements. The adverse effects of red mud were examined by ecotoxicity tests using test organisms from three trophic levels: Aliivibrio fischeri (luminescent bacterium), Sinapis alba (plant), Triticum aestivum (plant) and Tetrahymena pyriformis (unicellular animal). The results showed that red mud applied at 5% had positive effects on the degraded acidic sandy soil, significantly increasing soil pH, improving soil texture and water holding capacity. In addition, according to the ecotoxicological test results 5% w/w red mud had no significant adverse effects on the tested organisms as members of the soil ecosystem. CONCLUSION: The results demonstrated the beneficial effects of red mud as an ameliorant of acidic sandy soils under continental climatic conditions. (C) 2016 Society of Chemical Industry.