Avocado (Persea americana Mill., Family Lauraceae) is an important subtropical crop in the Americas where it has been cultivated for several thousand years. To investigate the bioactivities of avocado, which acts on bone formation, we prepared methanol extracts from the sarcocarp, peels, and seeds of avocado. The methanol extracts of peels and seeds showed higher bone-forming activity than avocado sarcocarp extracts accompanied by MC3T3-E1 osteoblast proliferation and alkaline phosphatase (ALP) activity. Additionally, the extracts of sarcocarp and peel from avocado also decreased tartrate-resistant acid phosphatase (TRAP) activity against differentiation of osteoclasts, derived from mouse bone marrow macrophages. The hexane fraction from avocado peels showed strong bone-forming activity accompanied by osteoblast proliferation and ALP activity (170.7${pm}$8.4%), and the ethyl acetate fraction from avocado peel decreased TRAP activity (5.2${pm}$0.3%) and differentiated osteoclasts at 50 ${mu}g$/mL. Therefore, avocado is expected to be a natural source for developing medicinal agents to prevent bone-related diseases, such as osteoporosis, by increasing osteoblast differentiation and reducing osteoclast activity.