Aim To investigate the changes of serum miR-24 and its target gene YKL-40 in diabetes mellitus (DM) with coronary heart disease (CHD) and explore its clinical significance as a predictive potential biomarker. Methods According to the coronary arteries angiography and diabetes diagnostic criteria, the study included 61 subjects with CHD subjects (n=34), DM+CHD subjects (n=27), and 32 negative predictive value of coronary angiography (control) in our affiliated hospital from October 2013 to June 2016. Gensini score was used to evaluate the severity of coronary artery lesions. Bioinformatic analysis and identification of serum miR-24 and its target YKL-40 were assessed using quantitative real-time PCR, ELISA after a bicinchoninic acid (BCA) assay, and receiver-operating characteristic (ROC) assays. Results miR-24 was especially gradually decreased in serum of CHD and DM+CHD patients compared with controls and reached to minimum in DM+CHD groups, and conversely, its target YKL-40 mRNA and protein levels were significantly increased in serum of CHD and DM+CHD patients and reached to maximum in DM+CHD groups. Furthermore, the area under the curve (AUC) and 95% confidence interval (CI) for the receiver-operating characteristic (ROC) analysis was 0.919 (95% CI:0.856～0.983) and 0.901 (95%CI:0.814～0.988), suggesting that the levels of miR-24 have high diagnostic values in distinguishing between DM+CHD and non-DM+CHD, or DM+CHD and CHD. Conclusions Serum circulating miR-24 was significantly decreased in patients with DM+CHD that had high clinical diagnostic value, indicating that miR-24 could be a potential biomarker for predicting diabetes mellitus with coronary heart disease.