An ultraviolet air sterilizer for disinfecting bacterium and virus includes a shell, a sandwich activated carbon cloth filter element, a nanometer titanium dioxide screen filter, an ultraviolet light source, a heat sinking kit, and a fan. The shell includes a shell body and a cover plate. The shell body is provided with an air inlet and an opening. The cover plate is provided with an air outlet. The sandwich activated carbon cloth filter element, the nanometer titanium dioxide screen filter, the heat sinking kit and the fan are arranged sequentially along an air path from the air inlet to the air outlet. The ultraviolet light source is configured for emitting ultraviolet light to the nanometer titanium dioxide screen filter. The air sterilizer has a compact small-sized structure and effectively removes ambient gaseous as well as particulate pollutants and kills micro-organisms harmful to health and well being.