Abstract: Objective To observe the influences of STAT3 antisense oligonucleotide on proliferation and apoptosis ofMCF-7 breast cancer cells.To study the effects of STAT3 antisense oligonucleotides on MCF-7 breast cancer cells in ovder to provide a new experiment evidence for breast cancer biological therapy. Methods The MCF-7 breast canner cell was transfected with STAT3 antisense oligonucleotide mediated by catholyte liposome.The cells growth and morphology were observed with a convert microscope.The proliferation of the cells was evaluated byMTT assay and the cell cycle was determined by flow cytometry.The expressions of total STAT3 protein and p-STAT3 protein were measured by western blot. Results The MCF-7 breast canner cell was transfected with STAT3 antisense oligonucleotide,which led to a sevies results including the inhibition of MCF-7 cell proliferation,the apoptosis of MCF-7 cell,the downregulation of STAT3 protein expression and phosphorylation,and the arrest at G1 phase. Conclusion STAT3 antisense oligonucleotides could inhibit MCF-7 cell proliferation,promote MCF-7 cell apoptosis,which may provide a new direction for the treatment of breast cancer.