An adhesive tape substrate production method disclosed in the present description includes the steps of: decreasing the amount of a sizing agent contained in a glass cloth by heat; impregnating the glass cloth for which the amount of the sizing agent has been decreased with a dispersion of a fluorine resin; and heating the impregnated glass cloth to a temperature equal to or higher than a melting point of the fluorine resin. Thus, an adhesive tape substrate including the glass cloth impregnated with the fluorine resin is obtained. This method are more productive of adhesive tape substrates and adhesive tapes than conventional methods. In addition, adhesive tape substrates and adhesive tapes for which the occurrence of defects in appearance are reduced can be produced.