In this study, two poly(acrylic acid)/alumina (PAA/alumina) nanocomposites with varied polymer loadings were prepared via in situ polymerization of preadsorbed acrylic acid. One composite would have a ~1/4‐monolayer polymer coverage, while the other had a ~2‐monolayer coverage. The produced composite materials were characterized in the adsorptive behavior of Pb2+ from aqueous solution. When there was less PAA produced in a nanocomposite sample, there was higher Pb2+ sorption capacity due to potentially less blocked alumina pores by in situ formed PAA. Isothermal and kinetic models for Pb2+ sorption were applied by considering the effects of the initial Pb2+ concentration and the contact time. The adsorption kinetics was best expressed using the pseudo‐second‐order equation. Through the isothermal studies, the maximum Pb2+ monolayer adsorption capacity of 167.79 mg/g was recorded for the composite with higher PAA loading.