Abstract: ObjectiveTo investigate the effectiveness of CDK4/CDK6 inhibitor p20 and p21 downregulating the migration and invasion of breast cancer cells. Methods Two CKI peptides (p20 and p21) were selected as CDK4／CDK6 kinase inhibitors.The human breast cancer cells (MDA-MB-231) were treated with CKI peptides (p20 and p21) (20μmol／L) for 24h respectively. The adhesion of MDA-MB-231 cell was measured with MTT assay. The monostratal wound healing test was used to determine the migration capacity of breast cancer cells. The changes in cell invasion were observed by the transwell invasion assay. Results After human breast cancer cells (MDA-MB-231) being treated with CKI Peptides (p20 and p21),the abilities of invasion and adhesion were decreased as compared with the control group (P<0.05).The migration capacity of breast cancer cells also significantly declined. Conclusion The CKI peptides (p20 and p21) （cell-penetrating peptides） can successfully declined the abilities of invasion and metastasis of breast cancer cells. Inhibiting the activation of CDK4／CDK6 kinase can restrain the metastasis and invasion of breast cancer cells.