Experimental data shows that ozone is effective in reducing airborne bacteria of unoccupied room. Over 90% of airborne bacteria could be reduced after ozonation. As viruses are generally more susceptible to ozone than bacteria, it could assume that all viruses are killed if large percentage of airborne bacteria are removed. Ozone is a gas that has good penetration capacity and powerful oxidizing power, thus its disinfection efficiency is superior to UV radiation and HEPA filter. As ozone disinfection is conducted in unoccupied room only and all the residual ozone will be decomposed after the treatment, ozone toxicity to human is therefore not a concern. Given the advantages of strong oxidizing power, good penetration capacity and no harmful residues left after the treatment, ozone is recommended to be used in disinfection of SARS-contaminated environments.