Objective To find out the potential pathomechanism of the CD3+ lymphocyte, CD68+ macrophage, matrix metalloproteinase (MMP)-2 and MMP-9 in abdominal aortic aneurysms (AAA). Methods The expression levels of the CD3+ lymphocyte, CD68+ macrophage, MMP-2 and MMP-9 were detected by immunohistochemistry and quantitatively analyzed in random 20 cases of AAA and 4 cases of control samples. Results The expression levels of CD3+ lymphocyte, CD68+ macrophage in the AAA group were significantly higher than in the control group [(100.44±105.82)/HPF vs. (0.55±0.41)/HPF, Z=-3.083, P=0.002; (233.02±195.30)/HPF vs. (5.05±1.70)/HPF, Z=-2.758, P=0.006]. Meanwhile, the expression MMP-2 and MMP-9 was significantly increased in the AAA group than in the control group(0.098 0±0.049 6 vs. 0.004 6±0.002 3, Z=-2.514, P=0.012; 0.024 8±0.014 6 vs. 0.030 0±0.022 2, Z=-0.308, P=0.002). Conclusion The high expression levels of the CD3+ lymphocyte, CD68+ macrophage, MMP-2 and MMP-9 may contributed to the pathogenesis of AAA. Key words: Abdominal aortic aneurysms; Matirx metalloproteinase; Inflammation