A histopathological study on the pathway of the inner ear involvement in experimentally produced Pseudomonas otitis media was done in 62 rats(Sprague Dawley). Otitis media was developed by inoculating Pseudomonas aeruginosa suspension(10⁷/ml, 10⁹ ml and 10¹¹/ml) into the bulla through the tympanic membrane. In the period of 3 days to 12 weeks after inoculation, the pathways of the inner ear involvement and the histopathological findings of induced labyrinthitis were studied with light microscope. 1) The incidence of serous labyrinthitis was 29% in 10⁹/ml and 7% in 10¹¹/ml animal groups, and that of suppurative labyrinthitis was 4% and 40%. 2) The hemorrhage in perilymphatic spaces was found in 81%. And it was considered as a result of increased venous pressure in sacrification or thrombophlebitis due to osteitis. 3) The pathways in serous labyrinthitis was round window membrane in 6 cases and thrombophlebitis in 4 cases. 4) The pathways in suppurative labyrinthitis was round window membrane in 10 cases of temporal bones and thrombophlebitis in 1 case and cochlear aqueduct through meningitis in 2 cases. The inner ear pathology in acute stage of experimental otitis media was mainly present in perilymphatic spaces with moderate degrees, and that in chronic stage was in labyrinthine bony capsule, modiolus, internal auditory meatus, including cochlear turns.