To investigate the clinicopathologic characteristics and mechanism of tissue injury caused by Klebsiella rhinoscleromatis (KR) infection.Thirty-three cases of rhinoscleromas in the nasal and pharyngeal region seen in this hospital from Jan. 1980 to Mar. 2000 were studied retrospectively. Warthin-Starry (W-S) stain was used to study all cases. Five cases were studied further with transmission electron microscope.W-S stain revealed a great number of KR in Mikulicz cells within the granuloma. Electron microscopy demonstrated a number of phagosomes in the cytoplasm of Mikulicz cells where many KR were found. A small number of other organelles such as endoplasmic reticulums and lysozymes were squeezed to the side of cells. There were many granular substances on the surface of intracellular bacteria, which were not found on the extracellular KR.KR is a facultative intracellular bacteria that is able to resist the digestion of macrophages and to proliferate in them. Formation of granulomas and fibrosis in KR infiltrated regions is the major cause of tissue injury.