This paper presents a detailed investigation on the effect of heat-treatment process on the highly ordered titanium dioxide (TiO2) nanotube arrays in connection with the photoelectrochemical (PEC) response and hydrogen evolution rate. TiO2 nanotube arrays have been systematically heat-treated to control the transformation of as-anodized TiO2 amorphous structure to crystalline anatase and rutile phases. In this study, single crystalline TiO2 anatase phase exhibited a higher PEC response and hydrogen evolution rate at 400 °C heat treatment. The photocurrent density increase was mainly attributed to the effective transport of photo-induced electrons within the single crystal anatase phase. However, polycrystalline anatase and rutile phases showed the fluctuation in lower photocurrent density upon heat treatment above 500 °C. The mobility of photo-induced electrons was obviously hindered due to the recombination losses in defect sites between the anatase and rutile phase.