BACKGROUND: As a new biodegradable metallic biomaterial, magnesium alloys with good bio-safety, degradability, mechanical strength and biocompatibility have been noticed in clinical practice. Recent studies mainly focus on the process and mechanism of degradation, biological safety and biocompatibility of magnesium alloys. Little is reported on the antibacterial properties of magnesium alloys. OBJECTIVE: To observe the antibacterial properties of novel magnesium alloys (Mg3Zn, Mg3Zn1Ag, Mg3Zn3Ag) in vivo. METHODS: The 12 of 15 Sprague-Dawley rats were implanted with different materials (Mg, Mg3Zn, Mg3Zn1Ag, Mg3Zn3A; three rats for each material) in the tibia of the hind limbs, respectively. Then, Staphylococcus aureus solution was injected at the incision of each rat. The remaining rats only given injection of Staphylococcus aureus solution were taken as controls. The above-mentioned treatments were repeated in another 15 Sprague-Dawley rats except injection of Escherichia coli rather than Staphylococcus aureus. The body temperature of the rats was continuously monitored within 14 rats after implantation. At post-implantation days 1, 3, 5, 10 and 14, the white blood cell count was measured. At post-implantation day 14, the rats were sacrificed and the secretions and tissues of the surgical site were taken for bacterial identification. RESULTS AND CONCLUSION: The body temperature of all the rats increased after bacterial infection, but the temperature of the rats implanted with magnesium and magnesium alloys was always lower than that in the two control groups given pure bacterial infection. Moreover, the increment in body temperature of the rats declined with the increasing Ag content in magnesium alloys. Routine blood test results showed that the number of white blood cells increased after bacterial infection, while the number of white blood cells in the magnesium and magnesium alloy groups peaked at 5 days after implantation, and then significantly reduced as compared with the control groups (P < 0.05). Furthermore, the increment in the cell number was reduced with the increasing Ag content in magnesium alloys. Bacterial culture results showed that S.aureus(+) in the Staphylococcus aureus infection group and E.coli(+) in the Escherichia coli infection group. To conclude, novel magnesium alloys exert marked antibacterial effects on Staphylococcus aureus and Escherichia coli. [ABSTRACT FROM AUTHOR]