Abstract: To study the anti-proliferation effect of λ-carrageenan oligosaccharides (λ-CO) on human umbilical vein endothelial cells (HUVECs) and expression of apoptotic relevant genes, the influence of λ-CO on HUVECs proliferation was measured by MTT assay; apoptotic rate, cell cycle distribution and the level of active caspase-3 of HUVECs were analyzed using flow cytometry; the mRNA level of apoptosis related genes was determined by RT-PCR. At a high concentration of 1 mg·mL^-1, λ-CO significantly inhibited the endothelial cell proliferation. Annexin-V FITC/PI double stain assay showed that when treated with 0, 0.8, 1 mg·mL^-1 of λ-CO for 24 h, cell apoptotic rates were (1.67±1.6)%, (11.48±2.4)% and (13.81±2.2)%, respectively, when treated for 48 h, cell apoptotic rates were (2.02±2.3)%, (13.84±1.9)% and (38.72±2.5)%, respectively, cell cycle assay showed the decrease of cells in Go/G₁ phase, and increase in S phase. Furthermore, we observed the level of active caspase-3 increased in a dose-dependent manner at 24 th and 48 th. RT-PCR results indicated that mRNA of TNFα, p53, caspase-8 and caspase-3 in cells increased after treated with λ-CO. λ-CO induce apoptosis of HUVECs in a dose-dependent way and arrests cells at S phase, which mainly due to the up-regulation of apoptotic genes such as TNFα, p53, caspase-8, caspase-3 and increase the level of active caspase-3.