The current study aims to investigate the relationship between plasma levels of miR-513a-5p and lipid metabolism and insulin resistance in patients with type 2 diabetes mellitus (T2DM) and nonalcoholic fatty liver disease (NAFLD). Two hundred patients with T2DM were selected, including 104 patients with NAFLD diagnosed by ultrasound and 96 patients without NAFLD. They were divided into combined group (T2DM/NAFLD) and control group (T2DM). Height, weight, blood lipid, and blood sugar were measured. Additionally, body mass index (BMI) and homeostasis model assessment of insulin resistance (HOMA-IR) index were calculated. RT-PCR was carried out to analyze the level of plasma miR-513a-5p. The correlation between plasma miR-513a-5p level and clinical indicators was analyzed by Pearson's correlation assay. Compared with the T2DM group, BMI, AST, ALT, TG, GGT, LDL-C, 2hPBG, Fins, 2hIns, HbAIc (%), and HOMA-IR were significantly increased in the T2DM/NAFLD group, and plasma miR-513a-5p levels were significantly decreased. Pearson's correlation analysis showed that miR-513a-5p was negatively correlated with ALT, LDL-C, 2h Ins, and HomA-IR. Receiver operating characteristic (ROC) analysis showed plasma miR-513a-5p could differentiate T2DM/NAFLD patients from NAFLD patients. Decreased plasma miR-513a-5p level may act as a potential biomarker for diagnosis of NAFLD in T2DM patients.