PROBLEM TO BE SOLVED: To provide a pearl nucleus decreased in load to a mother shell by improving affinity of the pearl nucleus to the living body and decreasing the weight, and also requiring no changing work of the nuclear, and to provide a method for processing cultured pearl which is capable of corresponding to requirement of weight decrease improving wear-feeling on a state of wearing the pearl on the body as an ornament so as to correspond to various utilizing form of the pearl and further capable of expanding the design versatility.SOLUTION: There is provided the water-absorbing pearl nucleus provided by forming a water-permeable coating film 2 on the surface of a granular molding 1 composed mainly of a water-absorbing resin, wherein the coating film 2 is formed of a material having rubber-like elasticity capable of regulating the swelling rate and volume of the granular molding. By providing, as a processing material, a pearl obtained by inserting the water-absorbing pearl nucleus into a mother shell for cultivation and cultivating, and forming a hole from the surface of the processing material to the pearl nucleus and pulling out the pearl nucleus through the hole to form a hollow part in the pearl, processing such as bleaching and toning can be performed against the pearl layer of the inside surface of the hollow part.
