AIM: To investigate the effect and mechanism of action of the nitric oxide synthase (NOS) inhibitor NG-nitro-L-arginine methyl ester (L-NAME) on invasion and metastasis of human colorectal cancer cell line SL-174T.METHODS: Human colorectal cancer cell line SL-174T was cultured and treated separately with four different dosages of L-NAME for 72 h. Nitric oxide (NO) production was measured with Griess reagent. The effect of L-NAME on invasion and migration of SL-174T cells were evaluated by using Transwell chambers attached with polycarbonate filters and reconstituted basement membrane (Matrigel).RT-PCR was performed to determine the mRNA levels of matrix metalloproteinase-2 (MMP-2) and tissue inhibitor metalloproteinase-2 (TIMP-2).RESULTS: L-NAME could significantly inhibit NO production of SL-174T in a dose-dependent manner. After being treated for 72 h with 0.2, 0.4, 0.8, and 1.0 mmol/L LNAME, respectively, the ability of the L-NAME treated SL174T cells to invade the reconstituted basement membrane decreased significantly (t = 8.056, P＜0.05;t= 14.467, P＜0.01;t= 27.785, P＜0.01;and t= 29.405,P＜0.01, respectively) and the inhibition rates were 10.29%,19.62%, 34.08%, and 42.23%, respectively. Moreover,L-NAME could inhibit migration of SL-174T cells, and the inhibition rates were 20.76%, 24.95%, 39.43%, and 46.85% for L-NAME at 0.2, 0.4, 0.8, and 1.0 mmol/L,respectively (t = 15.116, P＜0.01). In addition, after treatment with L-NAME, expression of MMP-2 mRNA was significantly decreased (t = 71.238, P＜0.01) and that of TIMP-2 mRNA was markedly increased (t = -13.020,P＜O.01).CONCLUSION: L-NAME exerts anti-invasive and antimetastatic effects on SL-174T cell line via downregulating MMP-2 mRNA expression and upregulating TIMP-2 mRNA expression.