The efficiency of raw wheat and soybean straws, corn stalks and corn cobs in removing different heavy metal ions from simulated contaminated water was studied. The investigated adsorbents have shown different adsorption capacities for copper, nickel, cadmium and lead ions. All of them, except for corn cobs, adsorbed copper ions well. Corn cob and wheat straw adsorbed cadmium and nickel ions well. As for lead ions soybean straw and corn stalks showed good adsorption capacity. In order to increase the adsorption capacities and decrease the leaching of extractive matters from all investigated biomasses, they were modified with (1) formaldehyde in acidic medium, (2) sodium hydroxide both with and Without previous modification with formaldehyde, (3) acid Solution or (4) only were water-washed. The effects of these treatments were evaluated in copper adsorption experiments. Treatments with formaldehyde, sulphuric acid and 5% NaOH were not advisable for investigated adsorbents. Adsorbents modification with 1% NaOH or water washing adsorbents gave good results, but the native (raw) materials were still quite efficient. In order to prevent organic matters leaching from biomasses during adsorption the washing of lignocellulosic materials is applied as it is the cheapest and the most suitable process.