Abstract: Objective To investigate relation of IL-18, collagen fibre(CF) and plaque stability in aorta atherosclerotic lesion. Methods morphology and content of CF in rupture of aorta atherosclerotic group(A group), non-rupture of aorta atherosclerotic group(B group) and normal aorta group(C group) by Massion's staining. Expression of IL-18 by immunohistochemical staining among three groups. Results Increasing and arranging turbulence of the CF was found in tunica intima, middle layer and tunica adventitia in A and B groups. Around necrosis of atheromatous plaque, the CF significantly increased and arranged turbulence, but the CF decreased or lacked in necrosis area of atheromatous plaque in A group. The CF significantly increased, arranged turbulence and extended to SMCs in necrosis of atheromatous plaque in B group. Arranging orderliness and no disruption of the CF was found in C group. Percent of CF content were significant difference among three groups (P <0.01). It showed the IL-18 strong positive in endothelial cells, inflammatory cells and necrosis of atherosclerotic plaques in A group, positive in B group and quite lowness or negative in C group. There were significant difference among three groups (P <0.05). IL-18 and CF were significant dependability among groups, respectively(P <0.05). Conclusions It was indicated IL-18 overexpression caused a marked decrease in collagen content and led to vulnerable plaque in aorta atherosclerotic lesion.