The main objective of this experimental study was the removal of methylene blue dye (MB) from an aqueous solution using modified grass waste (MGW). In this context, the grass wastes were subjected to a pre-treatment process with a 1% hydrogen peroxide solution in order to improve adsorption capacities. After modification of grass waste, some functional groups (-COOH and -OH) were efficiently introduced onto the surface of the adsorbent. These functional groups are very powerful in capturing MB dyes from an aqueous solution. Adsorption capacity of MGW for MB removal was investigated as a function of medium pH, MB and MGW concentrations, and particle sizes using batch adsorption experiments. The adsorbed MB concentrations increased with the increasing specific external surface area of the MGW, initial MB concentration, and pH, but decreased with increasing MGW concentration. The maximum adsorption capacity was 120 mg MB g MGW(-1) when the MGW concentration was 0.25 g L-1 with an average particle size of 64 mu m. The initial volumetric rate of adsorption was found as 44 mg MB L-1 h(-1) at a specific external surface area of 943 cm(2) g(-1) with the smallest particle size (53 mu m) tested.