Abstract: Corn cobs were impregnated with the pickle liquor from the surface treatment of iron and steel at ambient temperature for 24 h, dried at 393 K for 12 h and carbonized at 573, 773 and 973 K for 1 h to obtain magnetic activated carbons (MACs). The adsorption of methyl orange (MO) onto the MACs was investigated under different conditions. Results show that the surface area of the MACs increases with carbonization temperature from 423.5 to 784.76 m² g^-1. The MACs consist of hematite (Fe₂O₃) and magnetite (Fe₃O₄). The MAC obtained at 973 K has the highest MO monolayer adsorption capacity of 555.56 mg g^-1 at 298 K in a water sample containing MO dye. The adsorption is endothermic and obeys pseudo-first-order kinetics. The MACs can be easily separated from the dye water by an external magnet.