Introduction: To date, no study has investigated the antiresorptive property of lunasin. Hence, the present study aimed to assess the ability of lunasin to inhibit the osteoclast formation using RAW 264.7 cells. We hypothesized that lunasin is able to inhibit osteoclast formation. Methods: In the present study, the murine monocytic cell line RAW 264.7 was induced to differentiate into mature osteoclasts in the presence of recombinant receptor activator of nuclear factor kappa-B ligand. Tartrate-resistant acid phosphatase, a marker of osteoclasts, was used to identify osteoclasts. Cell lines were divided into different groups and exposed to different concentrations of 50 mu mol/L, 75 mu mol/L, and 100 mu mol/L active and inactive lunasin. The control group was RAW 264.7 cells with receptor activator of nuclear factor kappa-B ligand. Tartrate-resistant acid phosphatase positive cells of 3 or more nuclei, indicative of mature osteoclasts, were counted by 3 observers. The mean number of the data collected was analyzed using 1-way analysis of variance and the multiple comparison post hoc Bonferroni correction. Results: There was a significant difference in the reduction of osteoclast formation in all the active lunasin groups (P < .001) compared with the control group and the inactive lunasin group (P < .001). Conclusions: Considering the suppressive effect of lunasin on osteoclastogenesis, the use of lunasin as a potential antiresorptive agent can be evaluated in future studies.