Objective:To study the correlation between the occurrence of diabetes mellitus complicated with erectile dysfunction (DMED) and serum fibroblast growth factor-21 (FGF21) level, analyze the role of FGF21 in the occurrence of DMED, and explore its predictive and diagnostic value for DMED.Methods:61 male patients with type 2 diabetes in Tai′an Central Hospital from January 2017 to June 2018 were selected as subjects. They were divided into 2 groups: DMED group ( n=30) and type 2 diabetes mellitus group (DM group, n=31). And 32 healthy persons were selected as control group. The general data of all subjects were collected, physical examination, genital examination and blood sampling were carried out for biochemical analysis. The erectile function was measured by International Erectile Function Index-5 (IIEF-5) questionnaire, and serum FGF21 level was detected by automatic biochemical analyzer. The correlation between IIEF-5 score with FGF21 and other indicators were analyzed by Spearman correlation analysis. Multiple linear regression analysis was used to analyze the related risk factors affecting DMED. Receiver operating characteristic (ROC) curve was used to analyze the predictive value of FGF21 level for DMED. Results:(1) The serum level of FGF21 in the DMED group, DM group, control group were (112.5±9.2)pg/ml, (103.9±6.2)pg/ml and (91.9±3.9)pg/ml respectively, with significant differences (all P<0.05). (2) Spearman correlation analysis showed that IIEF-5 score was negatively correlated with FGF21, age, smoking, drinking, systolic blood pressure, diastolic blood pressure, glycated hemoglobin A1c (HbA 1c), fasting plasma glucose (FPG), total cholesterol (TC), total glyceride (TG), low density lipoprotein cholesterol (LDL-C), fasting insulin (FINS), homeostasis model insulin resistance index (HOMA-IR), and positively correlated with high density lipoprotein cholesterol (HDL-C) and testosterone( all P<0.05). The serum FGF21 level was positively correlated with smoking, drinking, systolic blood pressure, diastolic blood pressure, HbA 1c, FPG, TC, TG, LDL-C, FINS, HOMA-IR, and negatively correlated with HDL-C and testosterone ( P<0.05). (3) Multiple linear regression analysis showed that FGF21, HbA 1c, HOMA-IR and IIEF-5 were independent risk factors for erectile function (all P<0.05). (4) According to ROC curve, when the optimal cutoff value of FGF21 level was 102.75 pg/ml, the predictive sensitivity and specificity for DMED were 0.867 and 0.714, respectively. Conclusions:Serum FGF21 level is closely related to the occurrence of diabetes mellitus and DMED, which is an independent risk factor of DMED.