Hydrothermal derived titanates nanoparticles (HTN) have received considerable attention because of the onedimensional nanostructure, the simplicity for its synthesis, and band gap energy (Eg). Alkali titanates with general formula A2TinO2n+1 are commonly synthesized at high concentration of aqueous solution of NaOH or KOH, and relatively low temperature in the range of 100-250 °C. The microstructure consists of alternate layers of TiO2 octahedra and alkali ions, forming zigzag ribbons. The final microstructure of the titanate polymorph depends on the value of n, i.e. layered for 2<n>4, and tubular for n>6. Thus, the chemical composition of the resulting powder plays a major role in the final properties and potential applications of the material. The relative position of Eg with respect to the hydrogen electrode is the main disadvantage, because the material is active only under ultraviolet (UV) illumination. Thus, it is desirable that the HTN be activated under visible light conditions. Several works have reported the effect of the annealing temperature on the evolution of the crystalline phases, and microstructure of HTN, but few have reported the changes in the Eg. Amano et al. attributed the decrease in the Eg to the change of the chemical composition [1]. Allen et al. involved the formation of microstructural defects in the reduction of Eg [2]. Therefore, in this work is presented the microstructural characterization of the HTN particles annealed at different temperatures, and its relation with the changes in the band gap energy.