Lipopolysaccharide (LPS) can cause injuries to the vascular endothelium and induce cell apoptosis resulting in various vascular diseases. However, the relevant processes and molecular mechanisms have not yet been fully clarified. Chitosan oligosaccharide (COS) can protect cells, but there are only a few reports showing that it can effectively inhibit LPS-induced cell apoptosis. This study focuses on human umbilical vein endothelial cells (HUVECs). After cells were treated with LPS for 4-8 h, it was found by flow cytometry that the cell apoptosis ratio, and the reactive oxygen species and calcium concentration in the cells increased. Furthermore, using the patch clamp technique, it was observed that the large conductance calcium-activated potassium channel (BKCa) was activated at the same time. All phenomena could be reversed after pretreatment with COS for 24 h, showing that COS is capable of inhibiting LPS-induced cell apoptosis. The results of the assays on the action mechanism of COS show that it is capable of inhibiting the LPS-induced decrease of the Bcl-2/Bax ratio, increase of caspase-3 and activation of BKCa. Thus, one of the mechanisms of action of COS in the inhibition of cell apoptosis is to participate in the regulation of the BKCa channel. On the other hand, COS can inhibit the phosphorylation of LPS-induced p38 and accelerate the expression of O-GlcNAc glycosyltransferase, which indicates that COS can inhibit LPS-induced cell apoptosis through many pathways.