The effects of simulated microgravity on cell growth and extracellular matrix of chondrocytes have been examined by a light microscope and a scanning electron microscope using cultured chicken embryonic chondrocytes as the model. No notable difference of the cell density between the rotation group and the control group has been found. But during the same period, the growth spots of the rotation group were sparser than those of the control group. These results indicated that the lower level of cell development and differentiation happened in the rotation group. Observation by the scanning electron microscope showed that the extracellualr matrix decreased after rotating, and the fibres in the extracellular matrix were slighter and blurrier than those of the control group. It is concluded that the simulated microgravity can affect the secreting and assembly of the extracellular matrix. The possible mechanism for them is discussed.