A method is provided for manufacturing a stator of an electrical rotating machine. The method includes: impregnating a first winding head with a first composition that includes a heat-setting resin and a filler of a first particle size; impregnating conductive wires in a slot region with a slot-impregnating composition that includes a heat-setting resin and another filler of a second particle size smaller than the first particle size of the filler of the first composition; and impregnating a second winding head with a composition that includes a heat-setting resin and a filler of a particle size larger than the second particle size.