This study was aimed to investigate whether the thrombopoietin (rhTPO) may facilitate myelofibrosis or not. The modified Dexter culture system with various concentrations of rhTPO was used to culture the stromal cells in vitro; the proliferative activity of cells was detected by MTT method; the morphologic changes were observed by light and scanning electron microscopy; the staining changes of ALP, PAS, AS-D NCE and IV type collagen were observed by cytochemistry method; the changes of fibronectin, laminin and IV type collagen were assayed by immunohistochemistry method; the cell surface antigens were assayed by flow cytometry. The results indicated that rhTPO could promote the proliferation of stromal cells which was related to the concentrations of rhTPO. Proliferative activity of stromal cells increased with increasing of rhTPO concentration, and was not related to the exposure time. On day 3 stromal cells adhered to the wall, and became oval. On day 7 stromal cells turned to fusiform and scattered dispersively. On day 12 to 14 these cells ranged cyclically and became long fusiform. Cells covered 70%-80% area of bottle bottom at that time. By day 16 to 18 these cells covered more than 90% area of bottom and ranged cyclically. They displayed the same shape as fibroblasts. By light microscopy with Wrights-Giemsa staining, fibroblasts predominated morphologically, few macrophages, endothelial cells and adipose cells were found. There were no significant differences between experimental group and control group. On day 14 to 42 the adherent cells were positive with PAS staining, poorly positive with ALP and naphthol AS-D chloroacetate esterase (AS-D NCE) staining, and the difference in cytochemistry was not significant between two groups. When these cells were dyed with Masson's trichrome and Gomori's staining, neither collagen fibers nor reticular fibers were positive, but fibronectin, laminin, and collagen type IV appeared positive stronger in experimental group than those in control. The expressions of these molecules were not dependent on culture time. By scanning electron microscopy microvilli and fibers on cell surface appeared more and more, monolayer cells evolved into multilayer cells, and newly-formed fibroblasts appeared gradually as culture time prolonged. These alterations were not different among various groups. The expressions of CD34, CD45, CD105, CD106, and CD166 were not affected obviously by rhTPO. It is concluded that rhTPO had no effects on histochemical properties of stromal cells. Fiber staining and scanning electron microscopic examinations revealed that rhTPO can not facilitate fiber formation of stromal cells. But rhTPO may be able to augment the expressions of fibronectin, laminin and collagen type IV of stromal cells. Therefore it is still necessary to follow up the patients for a long time, who have received rhTPO therapy clinically.