Glucocorticoids is a synthetic steroid drug used widely in human life because this honnone has diverse effects in the treatment of disorders, syndromes, diseases such as pain, inflammation, asthma, arthritis, and causing immunosuppression (in the transplant),... However, glucocorticoids also causes many side effects. Osteonecrosis is one of the most common and serious complications. The treatment of osteonecrosis is not quite effective because early diagnosis is difficult and surgical methods Goint replacement) may be limited. This study investigated the effective prevention of osteonecrosis by bone marrow mononuclear cells transplantation. Adult mice were injected with dexamethasone (Dex) with weekly doses of 4, 6, 8 mg/kg for 8 weeks. At once, asparaginase (Asp) is used to enhance bone necrosis. Osteonecrosis was identified through staining method of bone tissue, analysis of the necrotic cells in the bone marrow by flow cytometry (FCM) and gene expression of osteocalcin, Runx2, BMP2 by RT-PCR. Results: in the H&E staining method, osteonecrosis rate increases together with Dex dose increasing. The dose of Dex 6 mg/kg was assessed effectively causing osteonecrosis, with osteonecrosis mice rate was 50 percent, death rate was 13.3 percent. The apoptosis and necrosis of bone marrow cells are also affected by increasing Dex dose (4.6, 5.3 and 9.7 percent respectively in the control, Dex4, Dex6). The expression of osteogenic genes also decreased, which induced by Dex. The effect of bone marrow mononuclear cell grafting after two weeks was detennined as a potential of preventing the progression of the disease.