Abstract: The present invention relates to the development of water purifying compositions based on magnetic nanoparticles decorated activated carbon nanocomposites which display both magnetic character as well as adsorbent characteristics. The addition of adsorbent to impure water containing dye as pollutant enables the fast adsorption of dye leading to discoloration of water whereas magnetic properties facilitates the rapid isolation of pollutant adsorbed nanocomposites powder from the purified water with the aid of a magnet. The present invention also provides a process for the development of such multifunctional adsorbent using a process which enables decoration of adsorbent with 5-50 weight % of magnetic nanoparticles, the enables the realization of magnetic adsorbent having saturation magnetization in the range 0.09 to 28.3 emu/g, dye removal efficiency of >99%, rapid decolourization of methylene blue (MB)/methyl orange (MO) dye polluted water in less than 1 min, magnetic separation time in the range <0.