The present invention provides a method for controlling the litter size of a pig, comprising the steps of: (a) determining the blood types of the pigs; and (b) breeding a pig having a heterozygous blood type and a pig having a homozygous blood type by using the blood types determined in step (a). The method for controlling the litter size of a pig, according to the present invention, analyzes the blood types of the pigs, and breeds the pig having an AO blood type and the pig having an OO blood type so as to restrain the formation of AA-type homozygous embryos, thereby preventing embryonic death, caused by a recessive lethal effect occurring at the point in time when thirty days after pregnancy have elapsed, such that the litter size of the pig can significantly increase.
