Abstract: The surface frce energy of solids is a characteristic factor which affects the surface properties such as absorption,wetting,adhesion, etc.A direct method for its measurement, however,has not yet been established.In this investigation,we developed a method for measuring the surface free energy and its components of glass fibres,which were untreated or treated with various silane coupling agents,by means of electrobalance,It was based on the measurement of the contact angle of a liquid L₁ to a solid S under another Liquid L₁ to obtain indirectly the surface free eusrgy of the solid.It can be seen from the result. that the surface free energy of glass fibers is decreased by being treated with s:ilane coupling agents and is. closely dependent on the structure of silanes.If the silane lxas polar function group, the surface free energy of treated glass fibers is high.If the silage has no polar group,the surface free energy is low.The fibres treated with the silane with double bond has m讨dle surface free energy.