Abstract: The present invention relates to a functional pillow for preventing positional head deformity of an infant. The functional pillow includes an inner foam member which is porous, an outer cover which encloses the inner foam member and includes a plurality of through-holes formed thereon, a head seating portion which is formed on at least one of a top surface and a bottom surface of a pillow body which includes the inner foam member and the outer cover in an eccentric position to allow a head to be placed thereon, and at least one layered auxiliary pillow which is inserted into the head seating portion and includes an auxiliary head seating portion of a different size formed on a surface. A degree of layering of the auxiliary pillow is different according to a head size.