Atmospheric-pressure, non-thermal, plasma jet produced by using helium gas has been studied for various applications. Especially, plasma applications for biological treatment are attracted and researched all over the world. In this paper, various kinds of cell culture mediums were irradiated plasma jet, and its components were analyzed. The results showed that irradiating plasma jet to cell culture medium could cause to change its pH, electric conductivity and so on. These results suggest that irradiating plasma jet might cause to change cell form and to kill them. Moreover, plasma jet generate UV light, it can be cause to kill cells. It found that irradiation time of plasma jet is very important factor to treat cells. © 2013 The Institute of Electrical Engineers of Japan.