In the present paper the effects of the fiber content and the interfaee On the linear thermal expansion coefficient of the uniaxial glass fiber and the carbon fiber reinforced epoxy composites have been studied in the temperature range from 123 to 415K．The results show that the transverse thermal expansioncoefficient of the composites are greater than that of the matrix itself when the fiber conten t V，=0.2 to 0.4 and the surface treatment seems to have no effect on the axial thermal expansion coefficient of the composites．The relation-ships between the fiber content and the axial thermal expansion coefficient can be described by Shapery’s equation．When the temperature is higher than the glass transition temperature of the epoxy matrix，the two transverse di

rection(X-and Y-axis) thermal expansion coefficients are quite different from those expected by Shapery's equation．The morphology shows that an epoxy resin layer existed between the laminas．The thickness of the resin layer depends on the surface treatment of the fibers，hence it make the difference between the two thermal expansion coeffi-cients in the two transverse direction．