An autopsy case of tyrosinosis was reported. The patient was a 5‐month‐old boy who had jaundice and hepatosplenomegaly since 10 weeks after his birth. Tyrosine blood level was 6.937 mg/dl and the level of p‐HPPA oxidase low. Neuropathologically, the cerebral lesions were characterized by a spongy state, vacuoles in neuronal cells and focal deposition of PAS‐positive substance in and around the axon. The electron microscopic examination revealed axonal degeneration and unusual deep cortical structure, possibly axons, containing numerous lysosomes, elongated mitochondria and MCB‐like bodies in unmyelinated axon. These facts were suggested to represent morphologic evidence of altered cellular metabolism, related to impaired tyrosine degradation.