An object of the present invention is to maintain good conditions of mother pigs and decrease the stillborn piglets and the death rate of piglets in breast-feeding period, so as to increase the productivity in pig farming.In a method for feeding pigs, by administering a Grifola-derived substance selected from one or more of dried Grifola, dried Grifola powder and a Grifola extract to mother pigs, particularly to postpartum mother pigs, good conditions of mother pigs can be maintained and the stillborn piglets and the death rate of piglets in breast-feeding period can decrease. As a result, the productivity in pig farming can increase.