Aim To observe the effect of Alisma soup on the expression of matrix metalloproteinase-9 and the correlation with ERK pathway on foam cell derived from rat peritoneal macrophages. Methods Foam cell model derived from rat peritoneal macrophages was established after induction with oxidized low density liprotein （ox-LDL） （50 mg/L） for 24h. The foam cells were intervened with 20% Alisma -containing serum for 24 h. They were stained by oil red O to observe foam cell formation. RT-PCR and Western blot was utilized to detect the expression of MMP-9. p-ERK and ERK protein was detected by Western blot. Results The foam cell model was established sucessfully after the stimulation with ox-LDL（50mg/L）. As compared with the control group，the expression of MMP-9 protein and mRNA in ox-LDL group were elevated. However，after the intervention with 20% Alisma soup-containing serum and U0126,the specific inhibitior of the ERK signaling pathway，the expression of MMP-9 protein and mRNA and P-ERK protein decreased significantly comparing with ox-LDL group. There was no change of ERK expression among groups. Conclusion Pretreating macrophage with ox-LDL can establish foam cell model derived from macrophages. Alisma soup can inhibit the expression of MMP-9 in foam cell，and the mechanism maybe has correlation with ERK signaling pathway.