The present study used water-electrode plasma discharge to increase the effect of bacterial inactivation in water for bioengineering and biotechnological applications. The water-electrode plasma discharge system was fabricated using a newly designed plasma generator and a highvoltage power supply. Water contaminated with Escherichia coli was treated with water-electrode plasma discharge for 0, 1, 2, 3, 4, 5, 10, 20 and 30 min. As a result, the colony-forming units (cfu) of E. coli were reduced with plasma treatment time, reaching nearly complete inactivation after 30 min. In addition, rapid generation of H 2 O 2 in the contaminated water was observed, which could mainly account for the effective bacterial inactivation. In conclusion, direct generation of reactive chemical species under water was successfully achieved by using a water-electrode plasma discharge system, which could be practically used to enhance bacterial inactivation in a variety of bioengineering applications. KEYWORDSWater electrode; plasma discharge; bacterial inactivation; hydrogen peroxide CONTACT Jinmu Jung jmjung@jbnu.ac.kr * These authors contributed equally to this work.