Nanosilver particles and microsilver particles were implanted into a rat's back muscle. The pathology and the local biocompatibility were observed and compared at days 7, 14, 30, 90 and 180 after implantation. A good biological effect was observed on days 7 and 14, both in rats treated with nanosilver particles and in rats treated with microsilver particles. A bad biological effect was observed at day 30, and the nanosilver-treated rats had more serious inflammation than the microsilver-treated rats.