In this study, mesoporous Al2O3@TiO2 nanocomposites were synthesized via two successive precipitation methods. Due to the coated TiO2 layer, the Al2O3@TiO2 exhibited a significantly enhanced efficiency for the removal of reactive black 5 dye (RB5). The morphology and compositional characteristics of Al2O3@TiO2 were investigated by TEM, HRTEM, XRD, EDS, FTIR, BET, and zeta‐potential analysis. TEM photos illustrated that TiO2 film covered Al2O3, XRD suggested compositional phases of γ‐Al2O3 and anatase TiO2, and BET measurement confirmed its characteristic of the mesoporous material. Al2O3@TiO2 was applied as an adsorbent to remove RB5 from aqueous solution, and the adsorption isotherms fitted well to the Langmuir isotherm model. The photocatalysis experiments confirmed that Al2O3@TiO2 had the good photocatalytic performance for degrading RB5 and the hydroxyl radical was the major active group. The UV–Vis adsorbance spectra demonstrated that this Al2O3@TiO2 could incompletely degrade RB5 dye under natural indoor light simultaneously when adsorption occurred. © 2018 American Institute of Chemical Engineers Environ Prog, 38: S230–S242, 2019