The study was designed to synthesize iron oxide/alumina nanocomposites and to investigate their application as an adsorbent to remove both fluoride and arsenic from aqueous solutions. The nanocomposites were extensively characterized by X-ray diffraction analysis, Brunauer–Emmett–Teller analysis, Fourier transform infrared spectroscopy and zeta potential analysis. The size and morphology of the particles were determined by scanning electron microscopy which revealed an average particle size of ~230 nm. The synthesized nanocomposites were stable for at least 4 h in static conditions as evidenced by particle size measurements. Batch sorption studies were carried out and sorption isotherms and reaction kinetics were analyzed. The nanocomposites followed the Langmuir isotherm model and fitted well with pseudo-second-order reaction for both As and F. The maximum sorption capacity of the nanocomposites for As(III), As(V) and F at pH 7 was 1,136 µg/g, 2,513 µg/g and 4 mg/g, respectively. The presence of F in the model water had a synergistic effect on As(III) and As(V) removal whereas the presence of As had no significant effect on F removal at pH 7. Furthermore, the nanocomposites demonstrated significant antibacterial activity at a concentration of 4 mg/mL with ~3 log reduction of Escherichia coli after 24 h. The results of the study showed that the synthesized nanocomposites can be a promising adsorbents for As and F removal in small-scale water systems.