Water hyacinth (Eichhornia crassipes) was found to have biosorption capacity for cationic dye, malachite green (MG) from aqueous solutions. The study was carried out under various experimental conditions such as dye concentration, adsorption dose, pH and temperature to assess the potentiality of alkali activated water hyacinth stems (AAWHS) for the removal of malachite green dye from waste-effluents. A high percentage of dye removal was observed with the decrease in the initial concentration of dye and increase in amount of adsorbent. Equilibrium isotherms were analysed according to the Langmuir models of adsorption, showing to be applicable with maximum monolayer adsorption capacity of 13.33 mg/g. The dimensionless factor, R_L of the malachite green dye, AAWHS isotherm revealed that the adsorption process is favorable in nature.