This paper presents a capillary discharge in water, which was applied to sterilize tiny apertures of medical equipments due to the penetration of dissolved sterilization agent in water. In order to obtain stable and energetic discharge for sterilization, a capillary dielectric tube was used as a barrier material. Discharges in the tube can generate high electrical fields, ultraviolet rays, as well as various chemically active species which can be utilized for sterilization and decomposition of toxins and bacteria in water. The sterilization results of Escherichia coli (E. coli) were successful after 1 hour of treatment.