Bovine coronavirus (BCV) and bovine viral diarrhea disease virus (BVDV) are associated with calf diarrhea and severe mucosal disease of bovine, respectively. It is quite difficult to eradicate these virus infections in cattle-breeding farms. In the present study, we examined the effect of electrolyzed anode-side water on proliferation of these viruses in vitro. Electrolyzed anode-side water was prepared by electrolyzing the water containing 0.12% of NaCl. Both viruses were treated with electrolyzed anode-side water for 1 min, and then they were separately inoculated to Madin-Darby bovine kidney cells and detected by RT-PCR (for both viruses) or hemagglutination assay (for BCV). After cultivation for 3 to 6 days, neither BCV nor BVDV were detected in the cells or in the culture supernatant fractions, indicating that electrolyzed anode-side water inactivates BCV and BVDV. Electrolyzed anode-side water prepared in this study showed a low pH value (about 3) and contained a low concentration of free effective chlorine (7.0 to 20.0 ppm). However, the viruses were inactivated with neither the solution adjusted at a low pH value with HCl nor those adjusted at a high pH value (above 9.0) contained a low concentration of free effective chlorine. These results indicate that antiviral effect of electrolyzed anode-side water may be synergistically depended on pH and a concentration of free effective chlorine.