To report a case of onychocytic carcinoma in China. A 76-year-old female patient presented with a subnail mass on her left thumb for 3 years. Skin examination showed thickening of the left thumb plate whose surface was partially yellow and black in color, slight curving of the distal plate, obvious telangiectasia under the nail plate, and verrucous hyperplasia under the nail plate and at the lateral edge of the nail plate. Histopathological examination showed that the tumor grew and infiltrated downward in clumps, with obvious keratosis and necrosis in the center of the mass, and many "squamous vortex" structures, atypical cells, and pathological mitotic figures could be seen. Immunohistochemical study revealed that HK31 and HK85 were positively expressed in the squamous vortex region, K6/K16 was positively expressed in the basal part of the tumor, and HK75 was strongly expressed in the whole tumor region. The diagnosis of onychocytic carcinoma was confirmed. The patient received surgical excision combined with 3 sessions of photodynamic therapy, and no recurrence was observed during 18 months of follow-up.