Objective Osteoclast numbers and activity are directly related to bone turnover and metabolism. This study aimed to investigate the effects of sheep bone marrow peptides (MP) and calcium?chelated MP (MP?Ca) on the formation and activity of RANKL?induced osteoclasts. Methods MP?Ca was prepared by a chelating reaction between MPs and CaCl ₂. RAW264. 7 cells were induced to osteoclasts by RANKL treatment, and cell proliferation was examined using the MTT assay. Induction was intervened by MP and MP?Ca to determine optimal concentrations and to investigate their effects on induction curves, TRAP activity, and the number of lacunae formed in bone slices. Results Under the induction system, on day 5, cultured cells were took on typical morphology of mature osteoclasts, TRAP staining was positive, resorptive pits formed, and the peak OD ₄₉₀value was achieved. The lowest OD ₄₉₀value was achieved when 10³μg/ mL MP or MP?Ca were added into the induction system on day 5. When 10³ μg/ mL MP or MP?Ca was added to the induction system, except on day 1, OD ₄₉₀values from days 2 - 8 were significantly lower than the blank group ( P <0. 05). In addition, the OD490 value and TRAP activity of the MP?Ca group were markedly lower than the MP group ( P <0. 05). Pit numbers in the intervention groups were notably lower than the blank group, and the number of lacunae in the MP group was significantly lower than the MP?Ca group ( P < 0. 05). All indices checked in the 17?β?estradiol group were lower than the intervention groups ( P <0. 05). Conclusions Although inferior to estrogen, both MP and MP?Ca inhibite the RANKL?induced formation and the resorptive activity of osteoclasts. Moreover, MP?Ca was more effective at inhibiting osteoclast formation than MP.