Currently, photocatalytic oxidation (PCO) is considered to be an effective process for removing and destroying low-level pollutants, which makes it a strong candidate for indoor air quality applications. Our study evaluated the titanium dioxide (TiO 2 ) filter media in controlling bioaerosols in a laboratory test chamber. The influences of microorganism species, relative humidity, and face velocity on the germicidal effectiveness of a TiO 2 -coated filter with 365 nm 8 W and 36 W blacklight irradiation were investigated. A Collison nebulizer generated Escherichia coli ( E. coli ), Bacillus subtilis ( B. subtilis ) endospores, yeast cells of Candida famata ( C . famata ) var. flareri , and spores of Penicillium citrinum ( P. citrinum ). The PCO control effectiveness was determined as the ratio, N S / N 0 , where N S and N 0 were the culturable concentrations collected by an Andersen one-stage sampler downstream of TiO 2 -coated filters with and without blacklight irradiation, respectively. Our results demonstrated that there were no significant differences in microorganism penetrations for TiO 2 -coated filters with and without blacklight irradiation. It was recommended that TiO 2 filter media used in this study did not perform as a good germicidal capability for airborne microorganisms.