AIM: To investigate the inhibitory and anti-metastatic effect of mutant p27 gene ( p27mt) on the growth of colorectal cancer xenografts in nude mice and its unerlying mechanism.METHODS: Inhibitory effect of p27mt gene on the growth of colorectal cancer xenografts was determined by measurement of tumor size before and after direct intra-tumoral injection of Ad-p27mt in a pre-established transplantation model of human colorectal cancer in nude mice. Cell cycle and apoptosis were detected by flow cytometry performed on single-cell suspension from an isolated tumor. Expression of MMP-9 in tumor tissue was detected by immunohistochemistry.RESULTS: The average sizes of transplantation tumors groups, respectively ( P < 0.05). The average proliferation control groups, respectively ( P < 0.05). The average control groups, respectively ( P < 0.01). The average MMP-9 expression rates were 20%, 75% and 66.7%in the Ad-p27mt, Ad-LacZ and control groups, respectively ( P < 0.01).CONCLUSION: p27mt inhibi t s the growth of transplanted tumor by blocking the proliferation of cancer xenografts and by promoting apoptosis of transplantated tumor cells, as well as decrease transplanted tumor metastasis.