We studied the effects of long-term (20-day) simulated microgravity (clinostatic exposure) and osteogenic differentiation stimuli on cultured mesenchymal stromal precursor cells isolated from human bone marrow. Clinostatic exposure significantly reduced proliferative activity of mesenchymal stem cells in comparison with the static and dynamic control, increased the number of large flat cells in the culture, and stimulated migration activity of cells. Phenotypic studies of surface antigens (CD90, CD54, CD106, CD105, CD34, CD45, class 1 HLA) during clinostatic exposure of mesenchymal stem cell cultures showed differences in their expression between experimental and control groups. Studies of osteogenesis of precursor cell showed that cell differentiation potential can be directed towards osteogenesis by a combination of clinostatic exposure and differentiation stimuli. The results confirm gravity sensitivity of human bone marrow precursor cells and open new vistas for understanding of the mechanisms of bone tissue loss in humans under conditions of space mission.