Estrogens are important regulators of bone cell function. Osteoblast-derived membrane type 1 matrix metalloproteinses (MT1-MMP) have recently been implied to play an important role in the process of bone resorption by proteolytically activating latent matrix metalloproteinase-2 (proMMP-2) at the cell surface and degrading tumor necrosis factor-alpha (TNF-alpha). In the present study, we observed the effects of 17beta-estradiol (E2) on MT1-MMP production and subsequent activation of latent matrix proMMP-2, and also proMMP-2 secretion in cultures of human osteoblastic MG-63 cells. Western immunoblot analysis showed that treatment with increasing doses of E2 in MG-63 cells caused a dose-dependent increase in expression of MT1-MMP protein. Confocal immunohistochemistry analysis also confirmed that E2 induced MT1-MMP synthesis in MG-63 cells. We found unexpectedly that although MT1-MMP synthesis was up-regulated by E2 in cultures of MG-63 cells, activation of proMMP-2 was unchanged, which can be attributed partly to the undetectable tissue inhibitor of metalloproteinase-2 (TIMP-2) protein in MG-63 cells by Western immunoblotting. ProMMP-2 production was also not influenced by E2. In conclusion, E2 induces MT1-MMP protein expression in MG-63 cells while it is not followed by proMMP-2 activation, E2 may suppress bone resorption by accentuated degradation of TNF-alpha which mediated through increasingly MT1 -MMP production in osteoblastic cells.