A wiring board prepreg manufacturing method of the present invention includes the step of depositing and adhering a porous layer made of aromatic polyamide or polyimide onto a heat resistant base material sheet according to a wet gelation process, and the step of impregnating at least one portion of a raw material composition of thermoset resin with insides of pores of the porous layer adhered to the heat resistant base material sheet. Moreover, it is preferable that the step of impregnating the base material composition of the thermoset resin includes the step of applying a raw material liquid of the thermoset resin containing a solvent to a surface of a base material, the step of removing the solvent from the applied raw material liquid so as to obtain a solid coating film, and the step of while heating the solid coating film, laminating and pressurizing the film together with the base material onto the porous layer so as to impregnate at least one portion of the solid coating film.