Novel magnetic fly ash/poly(acrylic acid) (FA/PAA) composite microgels were designed as a selective adsorbent toward Pb2+ ion based on the "treating wastewater with wastes" strategy. Magnetic fly ash (FA) containing magnetic iron oxides was selected as an inorganic cross-linker to produce magnetic FA/PAA composite microgels via an inverse suspension polymerization process, after being surface modified with polymerizable groups. The monomer, acrylic acid (AA), had been successfully grafted onto the magnetic fly ash to form the three-dimensional cross-linking skeleton of the beadlike magnetic FA/PAA composite microgels without any foreign organic cross-linker added. The microgels possessed high adsorption capacity and good adsorption selectivity to Pb2+ owing to the carboxyl groups from poly(acrylic acid) (PAA). The introduction of the magnetic fly ash could not only improve the strength stability of the FA/PAA composite microgels, but also provide them the ability of magnetic separation. Furthermore, the adsorbed Pb2+ could be easily desorbed, indicating the reusability of the magnetic fly composite microgels.