Abstract: Osteoclasts (OC) were isolated from long bones of 1 to 7 days old ducks. In the culture process, different concentration ratios of calcium (Ca) to phosphorus (P) (CCa : CP = 2∶1,1∶1,1∶2) were added to the culture system. The formation and activation of these OC were detected by phasecontrast microscopy, histochemical staining for tartrate-resistant acid phosphatase (TRAP) staining at the 1st and the 3rd day, and detection of lacunar resorption through scanning electron microscopy at the 7thday. For three days culture, the number of OC in experimental group was more than control group very significant. There was no difference between CCa∶ CP = 1∶1 group and CCa∶ CP = 2∶1 group.The difference among other groups was very significant at the 3rd day. The results demonstrated that CCa∶ CP = 2∶1 inhibits bone absorbing activity by inhibitng the formation and activation of OC.