Ultrastructures of the cutaneous xanthophores and formation of pigment granules in the goldfish, Carassius auratus L., are studied with electron microscope. The cutaneous xanthophores are observed only in dermis and pigment granules of these pigment cells are pterinosomes and carotenoid vesicles. By the differentiated level, pterinosomes are subdivided into 3 types; while type I pterinosomes have clear limiting membranes and contain some amorphous fine fibrous structures, type II pterinosomes have thick and densely aggregated fibrous materials. Type III pterinosomes have concentric lamellar structures in the granules. Pigment granules of the xanthophores are originated from the Golgi complexes and pinocytotic vesicles of plasma membrane as well as rER-rich cells among the chromatophores are presumed to be associated with the accumulation of pigment materials.