Purpose: Titanium dioxide (TiO2), a photocatalyst, is known to decompose various organic compounds under ultraviolet (UV) illumination by generating various radicals, which is useful for killing bacteria. The purpose of the present study was to evaluate the photocatalytic bactericidal effects of variously treated titanium surfaces on Streptococcus sanguinis SL1. Materials and Methods: Specimens were fabricated from grade 4 commercially pure titanium, 10 mm in diameter and 2 mm in thickness. Three different surfaces were prepared: anodized (AO) at 270 V, heat-treated (HT), and machined (MA). Surface analysis was performed using confocal laser scanning microscope, scanning electron microscopy, and thin-film x-ray diffractometry. The antibacterial activities were assessed by comparing adhesion and survival rates of S sanguinis on various surfaces under UV illumination. Results: The AO surface was rougher than the HT and MA surfaces. The AO surface showed TiO2 peaks of anatase structure, while the HT surface showed TiO2 peaks of rutile structure in x-ray diffractometry. HT and AO surfaces showed significantly decreased bacterial adhesion under UV illumination (AO and HT > control, AO > MA). In addition, bacterial adhesion decreased more significantly with extended UV illumination time. With respect to survival rates of bacteria, AO and HT showed a significant reduction over time compared to MA. The photocatalytic bactericidal effect was maximal on the AO titanium, followed by HT and MA. Conclusions: The photo-induced bactericidal efficacy of TiO2 films is dependent on their surface characteristics. Keywords: anatase, photocatalytic bactericidal effect, rutile, titanium dioxide, ultraviolet illumination