Background and Aim: Dielectric Barrier Discharge (DBD) cold plasma has efficient antibacterial activity on bacterial contamination at a short period of time and confirms its potential for routine used in clinical environment biodecontamination as an alternative to conventional disinfectant methods of water treatment. The goal of this study is to evaluated in vitro effectiveness of DBD cold plasma on clinically important opportunistic pathogens that identified from water samples which were: Legionella E.meningosepteca and S. paucimobilis growth and to study DBD effectiveness on survival bacterial cell after treatment. Methodology: 100-200 cfu/ml of Seven different environmental bacterial isolates belong to Legionella (4 isolates) E.meningosepteca(one isolate) and S. paucimobilis (two isolates) at species were subjected to eleven different exposure time of DBD cold plasma treatment rang from 15Sec to 300 Sec, and plated on suitable agar media. Results were quantified by viable count.