In approximately 30–40% of patients with diabetes mellitus (DM), the disease progresses to diabetic kidney disease (DKD), which can lead to end-stage renal disease. The study identified platelet-derived miR-145-5p and miR-6805-3p as potential biomarkers for the diagnosis of DKD. These miRNAs showed significantly higher expression in DKD patients compared to healthy subjects and DM patients, which was confirmed by bioinformatics and RT-qPCR analyses. The levels of miR-145-5p and miR-6805-3p are positively correlated with uric acid, serum creatinine, blood urea nitrogen, urinary albumin-creatinine ratio, cystatin C, platelet-lymphocyte ratio, and negatively correlated with estimated glomerular filtration rate, albumin, total cholesterol, LDL-C, blood glucose, and HbA1c. In addition, miR-145-5p expression was positively correlated with globulin. The levels of miR-6805-3p, but not miR-145-5p, were higher in patients with more advanced stage DKD. Research suggests that these platelet miRNAs may serve as biomarkers to diagnose DKD and monitor its progression.