Bio-applications of atmospheric pressure plasma have been widely studied in recent years. However, the devitalization mechanisms of micro-organisms by atmosphere pressure plasma have not been clearly explained. This paper was to find the possible sterilization mechanisms and define the major sterilization factors with the atmospheric pressure plasma jet. For the sterilization target, the Bacillus subtilis was selected. In this paper, a set of physical or chemical methods were used to characterize the following sterilization factors: heat, ultraviolet radiation, charged species and chemical reactive species generated by the plasma. It was found that the bacterial inactivation efficacy had a significant improvement when oxygen was introduced into the plasma jet system. Comparing with the result of sterilization, the inactivation process was dominantly controlled by synergistic actions of chemically active species and charged species, rather than heat, or ultraviolet radiation. (C) 2010 Elsevier B.V. All rights reserved.