In this study, single-crystal TiO2 nanorod (NR) arrays were used as the photoanodes of dye sensitized solar cells (DSSC). The post-annealing treatment was carried out in air, O2, N2 and vacuum atomsphere. X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) have been used to characterize the structure, morphology and crystallity of these samples. Although the nanorod arrays which undergo annealing remained the single-crystal structure without any change in the morphology, considerable improvement in the nanorod solar cell performance was obtained. The high efficicency of 4.42 % was achieved in the cells containing nanorods which were annealed in air at 500 °C for 30 min. In comparison, the cell fabricated using TiO2 samples without post- annealing treatment exhibited a low efficiency of just 2.1 %. Such a large improvement (280 %) was mainly attributed to the faster electron transport and the lower charge recombination rate after annealing due to an increase of the depletion width. Otherwise, the cell performance improvement may result from an enhancement in the adhension and electrical contact at the TiO2/FTO interface. The in-depth study shows that the solar cell efficiency was strongly dependent on the annealing ambience, too.