We develop "autologous bone marrow cell infusion (ABMi) therapy" for the treatment of human decompensated liver cirrhosis and confirm the efficacy and safety of this treatment in multicenter clinical studies. With the goal of further expanding the applications of ABMi, we first cultured human bone marrow cells and then determined whether a cell fraction found to be effective in improving liver fibrosis can be amplified. Cells harvested after two passages (P2 cells) consistently contained approximately 94% mesenchymal stem cells (MSCs); conversely, the cells harvested after only medium change (P0 cells) contained many macrophages. MSCs (2.8 × 10(8)) in P2 cells were harvested from 3.8 × 10(8) bone marrow-derived mononuclear cells after 22 days. DNA-chip analysis also showed during the culturing step that bone marrow-derived cells decreased with macrophage phenotype. The infused 5 × 10(5) P2 cells significantly improved liver fibrosis in the nonobese diabetic/severe combined immunodeficient (NOD-SCID) mouse carbon tetrachloride (CCl4) liver cirrhosis model and induced the expression of matrix metalloproteinase (MMP)-9 and suppressed expressions of alpha smooth muscle actin (αSMA), tumor necrosis factor alpha (TNFα) and transforming growth factor beta (TGFβ) in the liver. Cultured human bone marrow-derived cells (P2 cells) significantly inhibited liver fibrosis. The increase of MMP-9 and suppressed activation of hepatic stellate cells (HSCs) through the regulation of humoral factors (TNFα and TGFβ) contribute to the improvement of liver fibrosis by MSCs comprising about 94% of P2 cells. MSCs in cultured human bone marrow-derived mono-nuclear cells (BM-MNCs) proliferate sufficiently in cell therapy, so we believe our cultured bone marrow-derived cell therapy can lead to expanded clinical applications and enable outpatient therapy.