Biosorption of hexavalent chromium onto green alga (Zygnema) was studied from aqueous solutions. Alga was collected from pond of village Thaska near Hissar ,Haryana and from this alga two type of biosorent was prepared (a)-Treated Zygnema (soaked in 1/ formaldehyde solution) (b) -Untreated Zygnema . Biosorption equilibrium was established in about 80 min. The surface properties of the microalgae preparations was varied with pH 2 -12 and maximum absorption of chromium ions on the microalgae preparations was obtained 80 % at pH 2 with treated alga and 63% with untreated alga . The biosorption of chromium ions by the microalgae preparations increased as the initial concentration of chromium ions increased in the medium. The maximum biosorption capacities of both alga was treated at optimum pH 2 with different concentration 10-50 ppm with variable dose 0. 2-1.2 gm with variable time 20-80 min. Equilibrium concentration (qm) and dissociation constant (Kd) were calculated by fitting the experimental data with the Langmuir isotherms. The chromium adsorption data were analysed using the first- and the second-order kinetic models. The experimental results suggest that the second-order equation is the most appropriate equation to predict the biosorption capacities of all the biosorbents.