To provide a evaluation method capable of evaluating a property for impregnating a glass woven fabric into a resin by a unified method, effective in carrying out inspection of quality of glass woven fabric and effective in feeding stable products by measuring impregnation of the resin into the glass woven fabric by transmitted light of a microscope.

A glass woven fabric is impregnated into a solvent-free resin which is liquid at a normal temperature (preferably an epoxy resin which is liquid at normal temperature, e.g. a bisphenol A type epoxy resin) and the treated glass woven fabric is put on a glass plate and time required until the resin is impregnated into the glass woven fabric and number of foam after impregnation are measured by transmitted light of a microscope. Furthermore, after the resin is packed into a container, the resin is defoamed in vacuum to remove foam in injection and a time required for impregnating the glass woven fabric into the resin is preferably controlled to be within the range of 2-20sec.