During the last decade the use of titanium dioxide has been the focus of water purification studies for photocatalytic degradation of organic compounds. Various studies have shown that TiO2 photocatalysis is a very efficient process for removal (by mineralization) of a large variety of hazardous chemicals. However, the potential use of this technology for water disinfection has been essentially unexplored. Only several papers described the photocatalytic destruction of microbial cells, such as E.coli bacteria, MS2 bacteriophages and recently B.fragilis phages, D. radiophilus. In this study, two bacilli strain spores (B. subtilis and B. cereus) were tested for photocatalytic inactivation in water as simulators of B. anthracis spores. B. subtilis was selected for its high resistance to disinfection and B. cereus for its phylogenetic proximity to B. anthracis. Two ultraviolet (UV) sources were used: a monochromatic UV lamp with an irradiation intensity of 7mW/cm2 at 365nm; and, natural sunlight (irradiation intensity at 365nm of ~ 4 mW/cm2 between 12:00 and 14:00 hours). TiO2 at 0.25g/L was found to be the optimal concentration needed for the reduction of four orders of magnitude in B. subtilis spores viability after irradiation for 300 minutes. B. cereus subjected to similar photocatalysis conditions was reduced by five orders of magnitude revealing lower endurance to this process. Comparison of artificial and natural (sunlight) UV irradiation source on B. subtilis resulted in increased inactivation of 5 orders of magnitude in favor of sunlight. Combined inactivation by photocatalytic process (UV 365nm) and detrimental activity of UV at 265nm can explain this result. There was no difference between the two irradiation sources when B. cereus was tested. Under both irradiation types, B. cereus was reduced by four orders of magnitude during 300 minutes time interval. Additional experiments including TiO2 concentration, irradiation intensity, water depth, initial spore number, etc. were performed. Taking into account that B. anthracis spores have hydrophobic properties, the photocatalytic process seems to be the method of choice in water disinfection eliminating the possibility of byproducts formation such as halogens. Includes 19 references, table, figures.