In this study, the novel polysaccharide SPS markedly repressed the proliferation of cancer cells, and induced the mitochondria-mediated intrinsic apoptosis in A549 lung cancer cells, as verified by loss of mitochondrial membrane potential, generation of intracellular reactive oxygen species, an increase in the ratio of Bax/Bcl-2 and the activation of cleaved caspase-3, caspase-9 and PARP. This evidence concerns the gene CASP9 and cancer.