After being examined by radiology, 30 chickens with experimental and natural osteopetrosis (OP) were selected for electron microscopy to make clear the relationship between radiological lesions and ultrastructural appearances. Fourteen cases were positive (+), 4 cases were moderate (++), 6 cases were strong (+++), 3 cases were suspicious (±), and 3 cases were negative (-) control. Electron micrographs of tibiae from 30 cases were examined. Bones of the 3 controls were ultrastructurally normal. Virions were observed in suspicious cases and positive cases (+, ++, +++). In size, morphology and ultrastructure, they resembled avian type C oncoviruses. The observation provides pathogenic evidence for OP radiological diagnosis. The OP suspicious cases and positive cases (+, ++, +++) had ultrastructural changes characterized by osteocyte necrosis, enlarged bone lacunae and vascular lesions etc. The correlation between radiology and electron microscopy provided ultrastructural evidence for OP radiological diagnosis.