This study investigated the effects of pressurized steam-treated Corni Frutus (PSC) extract on osteoblast differentiation and osteoclast formation. The osteoblast differentiation effect of the extract was evaluated by measuring cellular alkaline phosphatase (ALP) activity, cell matrix ALP staining, alizarin Red S staining and von Kossa staining on proliferating MC3T3-E1 osteoblast cells. The results confirmed that ALP activity, cell matrix ALP staining, alizarin Red S staining and von Kossa staining were all increased as proliferation increased from 1 to 14 days, without cytotoxicity. The osteoclast formation effect of the PSC extract was evaluated by measuring the cellular tartrate-resistant acid phosphatase (TRAP) activity and cell matrix TRAP staining on receptor activator of nuclear factor kappa-B ligand (RANKL)-induced RAW264.7 osteoclast cells. Treating RAW264.7 cells with RANKL for 7 days increased matrix staining for TRAP and cellular TRAP activity. The PSC extract decreased these changes in a concentration-dependent manner. Therefore, PSC is expected to be a natural source for developing health functional foods and medicinal agents to prevent bone-related diseases, such as osteoporosis, by increasing osteoblast differentiation and reducing osteoclast activity.