Abstract: Objective To investigate the expression levels of cytoskeleton-related protein SM22α in gastric cancer or adjacent normal gastric mucosa tissues. Methods RT-PCR and Western blotting were performed to detect SM22α mRNA and protein levels in gastric cancer tissues and adjacent normal gastric mucosa tissues. RT-PCR and zymography were used to detect MMP9 mRNA level and activity in gastric cancer tissues and adjacent normal gastric mucosa tissues, respectively. Results Both SM22α mRNA and protein levels in gastric cancer were significantly lower than that in adjacent normal gastric mucosa tissues (P<0.05). The expression and activity of MMP9 in gastric cancer cases were signifi cant higher than that in adjacent normal gastric mucosa tissues (P<0.05). A negative correlation was found between SM22α protein level and MMP9 activity in gastric cancer tissues. Conclusion SM22α is downregulated in gastric cancer. SM22α may probably inhibit metastasis through negative regulation of MMP9 expression in gastric cancer.