Abstract:This paper studies the protecting effects of Magnesium Lithospermate B(MLB) on aortic endothelial cells of human beings in a low temperature cell system in space. Aortic endothelial cells cultured in the low temperature cell system were on board of the No. 22 recoverable satellite. After 18-day's flight, cells were harvested, counted and stained by Giemsa. Comparing with the control group, the cells treated with Magnesium Lithospermate B are found to be in better conditions in morphology and proliferation. Magnesium Lithospermate B can improve the living condition of endothelial cells in spaceflight and reduce the damage to the cells from space radiation, micro-gravity and magnetic microfield.