Abstract: The method and nanocomposite for treating wastewater provides a method of treating aniline-containing wastewater with a magnetic nanocomposite. Nickel nitrate, iron nitrate and citric acid are dissolved in deionized water to form a metal nitrate and citric acid solution, which is then pH balanced. The pH balanced solution is then heated to form a gel, which is then ignited to form powdered NiFe2O4. Nanoparticles of the powdered NiFe2O4 combustion product are then mixed with multi-walled carbon nanotubes to form a magnetic nanocomposite, such that the magnetic nanocomposite includes approximately 75 wt % of the multi-walled carbon nanotubes and approximately 25 wt % of the NiFe2O4. The magnetic nanocomposite may then be mixed into a volume of aniline-containing wastewater for adsorption of the aniline by the nanocomposite. A magnetic field is then applied to the mixture to magnetically separate the magnetic nanocomposite and the adsorbed aniline from the wastewater.