Eggshell-powder as reactant react with AgNO₃ and NaBH₄ through ultrasonic reduction method to prepare the eggshell-powder nanosilver. The eggshell-powder nanosilver morphology and morphology changes of treated bacteria were characterized by using Scanning Electron Microscope (SEM). And its antibacterial properties were characterized by the microorganism meathods. The results showed that silver nanoparticles of eggshell powder had strong bactericidal effect on Escherichia coli, Staphylococcus aureus, Bacillus subtilis and Candida albicans etc. And the minimum inhibitory concentration (MIC) of this four bacterias were 1.5,3.0,3.0,6.0 mg/L and minimum bactericidal concentration (MBC) were 6, 12, 12, 24 mg/L.