AIM:To explore the protective effect of morinda officinalis oligosaccharides monomer HexB on hy -poxia/reoxygenation(H/R)-induced injury in human umbilical vein endothelia cells(HUVECs).METHODS:HUVECs were treated with HexB,4-phenylbutyric acid(4-PBA)and thapsigargin(TG),respectively.The cells were divided into control group,HexB group,H/R group,HexB+H/R group,4-PBA+H/R group,TG group and HexB+TG group.The cell viability was measured by CCK-8 assay.The apoptotic rate was detected by flow cytometry.Western blot was used to determine the protein levels of endoplasmic reticulum stress(ERS)related molecules chaperone protein glucose-regulated protein 78(GRP78),C/EBP homologous protein(CHOP),apoptosis-related protein caspase-12 and phosphorylated c-Jun NH2-terminal kinase(p-JNK).RESULTS: The viability of HUVECs was reduced in H/R group and TG group(P<0.05),increased in HexB+H/R,4-PBA+H/R and HexB+TG group(P<0.05).The apoptotic rate,the protein levels of GRP78,CHOP,caspase-12 and p-JNK were increased in H/R group and TG group(P<0.05),weakened in the HexB+H/R group(P<0.05),4-PBA+H/R group and HexB+TG group(P<0.05).No significant change in the apoptotic rate,cell viability,protein levels of GRP78, CHOP, caspase-12, p-JNK between HexB +H/R group and 4-PBA+H/R group was observed.CONCLUSION:HexB attenuates HUVECs injury caused by H/R through suppressing ERS and ap-optosis.The possible mechanism may be involved in the apoptotic pathways related to GRP 78,CHOP,caspase-12 and p-JNK.