ObjectiveTo compare the serum contents of 14,15-dihydroxyeicosatrienoic acid (14,15-DHET), a stable metabolite of epoxyeicosatrienoic acids （EETs), between senile diabetic patients with and without nephropathy and healthy controls, and to analyze the relationship of their contents with vascular endothelial dysfunction. MethodsWe conducted a case control study, which included 60 healthy senior citizens (group A), 78 senior diabetic patients with no clinical evidence of nephropathy (group B), and 58 senior diabetic nephropathy patients (group C). Serum levels of 14,15-DHET, 6-keto-PGF1α (a stable metabolite of prostaglandin) and TXB2 (a stable metabolite of thromboxane A2) were measured using ELISA kits. Meanwhile, the parameter of blood glucose and lipid were also examined. The endothelium-dependent vasorelaxation (EDV) and non-endothelium-dependent vasorelaxation (NEDV) in the brachial arteries were determined by Color Doppler Ultrasound. ResultsCompared with group C, group A and B had significantly lower serum levels of 14, 15-DHET and 6-keto-PGF1α , and values of EDV and NEDV（P<0.01）, and had significantly higher levels of blood hemoglobin A1c (HbA1c), triglyceride, cholesterol, and TXB2 , urine protein albumin, and values of TXB2/6-keto-PGF1α and TXB2/14，15-DHET（P<0.01）. The level of 14,15-DHET was negatively correlated with the course of disease, the levels of HbA1c, TXB2, triglyceride and cholesterol, and the ratios of TXB2/6-keto-PGF1α and TXB2/14,15-DHET; and it was positively correlated with the values of EDV and NEDV in senile diabetic patients with and without nephropathy. ConclusionOur results indicated that serum 14，15-DHET level is decreased during the early stage of senile diabetic patients with and without nephropathy. Like PGI2, 14，15-DHET may also serve as a biomarker for the impairment of EDV and NEDV in senile diabetic patients with and without nephropathy.