An oligosaccharide BBPW-2 was isolated and purified from Bombyx batryticatus, its molecular weight was 2.0 × 10(3)Da, and its structure was elucidated by compositional, methylation and NMR analysis. Our results showed that BBPW-2 consisted of β-D-(1 → 2,6)-glucopyranose and β-D-(1 → 2,6)-mannosyl units serving as the backbone, α-D-(1 → 2)-galactopyranose and α-D-(1 → 3)-mannosyl units as branches, and α-D-Manp and β-D-Glcp as terminals. The in vitro inhibitory activity of BBPW-2 was measured using MTT and and crystal violet assays, which suggested that BBPW-2 had direct cytotoxic effects on the cancer cell lines HeLa and HepG2 (particularly HeLa cells), and had a long-term antiproliferative effect on MCF-7 cells, respectively. Apoptosis and cellcycle analysis of HeLa cells showed that BBPW-2 induced cellcycle disruption in the G0/G1 and G2/M phases accompanied by an impressive increment of early apoptotic cells and late apoptotic and necrotic cells. These results suggest that BBPW-2 could be a potential chemotherapeutic drug and its antitumor effects deserve further study.