To provide a method for surface treating a glass cloth capable of improving the impregnation property of a resin in the process of a prepreg forming and also aiming at the improvement of a moisture absorption resistance by surface treating the glass cloth with a treating liquid containing a surfactant having a specific HLB value and a silane coupling agent.

This method for surface treating a glass cloth is to immerse the glass cloth in a treating liquid containing 0.05-0.5wt.% preferably 0.1-0.3wt.% surfactant having ≤8, preferably 5-8 HLB value such as a polyoxyethylenenonylphenyl ether, 0.03-0.3wt.% surfactant having 13-15 HLB value as a dissolution assistant such as a polyoxyethyleneoctyl ether, and 0.1-20wt.% preferably 0.3-1.0wt.% silane coupling agent, and dry after squeeze the cloth to obtain the cloth attached with 0.03-0.1wt.% and 0.1-0.2wt.% of the above surfactant having a low HLB value and the silane coupling agent, respectively.