In order to investigate the mechanism of antibacterial effect of electrical stimulation on bone and joint infection, 5, 50 and 500 µA constant currents were passed through the silver electrodes and stainless electrodes on the Brain Heart Infusion agar culture plates which contained Staphylococcus aureus, Pseudomonas aeruginosa, and Lscherichia coli. After 24 hours of incubation, the widths of inhibitory zone around the electrodes were measured. The broth dilution susceptibility test was also used to verify the antibacterial effects of electrically generated silver in the Brain Heart Infusion broth. The results were as follows. 1. Silver anodes using constant currents manifested antibacterial effects definitely on the three bacterias, but stainless anodes showed none. 2. Antibacterial effects of silver anodes on the three bacterias increased in proportion to current density. However, antibacterial effects were negligible when current density was under 2 nA/mm². 3. When current density was between 6.6 and 660 nA/mm², there were no statistically significant differences in the antibacterial effects among 5, 50 and 500µA constant currents. 4. The culture broth containing silver ions generated by constant current electrolysis also manifested antibacterial effects. The retentate showed stronger antibacterial effects than the filtrate. Form these results, following conclusions were drawh. 1. The antibacterial eff ct of silver electrode using constant current was due to silver ions rather than electricity itself. 2. The substance which showed most effective antibactericity effects was silver complex larger than 2,000 m.w. and heat-unstable.