To investigate the combined effect of kappa-selenocarrageenan (KSC) and paclitaxol (Taxol) on MCF-7 cells in vitro. The cytotoxic effect of both drugs on MCF-7 cells was measured by MTT assay, and the King’s principle was used to evaluate the interaction of drugs combination. KSC and Taxol alone have significant growth inhibitory effects on HepG-2 cells in dose- and time-dependent manners, and the combination groups show more remarkable anti-proliferative activities than the two drugs alone. The IC50 values of KSC and Taxol alone on HepG-2 cells for 72h are 48.445 mg/L and 2.592 nmol/L, respectively. While combining with 30 mg/L KSC, IC50 value of Taxol decreases sharply to 0.353 nmol/L. Q values of their combination are 0.908~1.051, which demonstrates additive effect. In short, selenium polysaccharide has striking inhibition effect on MCF-7 cells and can enhance efficacy of chemotherapeutic agents and reduce their side effects.