The study was aimed to isolate and establish mesenchymal stem cell line from adult murine bone marrow as well as to identify its biological characteristics and differentiation potential. Bone marrow cells (BMCs) were collected by flushing the femurs and tibias of 4 - 5-week-old male C57BL/6 mice, and were inoculated at a concentration of 1 x 10(6)/cm(2). mMSCs were isolated, enriched and expanded by using bone marrow adherant culture and monoclonal culture. The characteristics of the cells, such as morphology, growth pattern, cell cycle, phenotype, karyotype and multipotent differentiation potential, cytogenetic stability and tumorigenesis were determined. The results indicated that the cell population consisted of spindle- and star-shaped cells, they were highly positive for CD29, CD44, Sca-1, MHC-I, moderate positive for CD13, CD90.2 and negative for CD117, CD45, Flk-1 and MHC-II. mMSCs could be induced to differentiate into adipocytes, osteoblast cells and chondrocytes. It is concluded that mMSC can be isolted, expanded and enriched by using bone marrow adhcrent culture and monoclonal culture. No tumor formations are observed for 3 months in nude mice after subcutaneous injection. mMSCs retain their properties after at least 30 passages in culture as well as from frozen stocks.