The investigation of the metal oxide/inorganic ion interface at the atomic level represents a fundamental issue for the understanding of chemical and physical processes involved in several fields such as catalysis, adsorption, directed synthesis and the mechanistic study of crystal growth. In this paper, a combined hydrothermal synthesis and computational approach based on DFT theory is adopted to investigate the effects of sulfate ions on the final morphology of γ-AlOOH. The quantum mechanical calculations reveal that the sulfate ions interact with γ-AlOOH facets through surface hydroxyls and act as a morphology-directing agent. The adsorption type and chemical bonds between the sulfate ion and γ-AlOOH are discussed. The formation of nanosheets and nanorods of γ-AlOOH is controlled by thermodynamic factors. Moreover, the HR-TEM images reveal the growth directions and exposed planes of boehmite, indicating an oriented-aggregation process which is consistent with the DFT calculations. Overall, all the morphologies of boehmite suggested by the calculations are confirmed by experimental results.