The anti-tumor activity of the exo-polysaccharide component REPS2-A metabolized by Rhodotorula mucilaginosa CICC 33013 was studied. The exo-polysaccharide component REPS2-A was inhibited by tetramethylazole blue (MTT) method in 10 common cancer cells including blood cancer cell K562, gastric cancer cell BGC823, gastric cancer cell SGC7901, gastric cancer cell MKN28, liver cancer cell HepG2, BEL7402, Hep3B, pancreatic cancer cell HS66T, breast cancer cell SKBR3, and cervical cancer cell HeLa. The results showed that the exo-polysaccharide component REPS2-A had a good inhibitory effect on HepG2 cells. By studying the optimal concentration and time effect of exo-polysaccharide component REPS2-A on HepG2 cells, the growth inhibition and its mechanism of exo-polysaccharide component REPS2-A on HepG2 cells were investigated. The results showed that when the concentration of exo-polysaccharide component REPS2-A was 1 mg/mL, the inhibition rate of HepG2 in liver cancer cells was higher than that in IC50, and the inhibition effect was significantly better than that in other concentrations. The spontaneous apoptosis rate of HepG2 was 0.40%. When the concentration of exo-polysaccharide component REPS2-A was 1 mg/mL, the apoptosis rate of HepG2 was 77.70%, 88.18% and 97.08% after 24, 48 and 72 h treatment, respectively. Exo-polysaccharide component REPS2-A could effectively inhibit the proliferation of liver cancer cells, cause HepG2 block in the G1/S phase, and induce HepG2 apoptosis in liver cancer cells with dose effect.