Aim To find risk factors of contrast-induced nephropathy (CIN) after percutaneous coronary intervention (PCI) in elderly diabetic patients with acute coronary syndrome (ACS). Methods 134 cases of elderly diabetic patients with ACS (≥65 years old) was involved in this study. In the same period, 145 cases of PCI patients without diabetes were used as controls. The age, preoperation brain natriuretic peptide (BNP), ejection fraction, 25 hydroxyvitamin D, estimated glomerular filtration rate (eGFR), blood albumin and so on were compared between the two groups. Multifactor logistic regression analysis was used to find risk factors of CIN. Results 17 cases of CIN were found in 134 cases of patients with diabetes after PCI, the incidence was 12.6%. In 145 elderly patients without diabetes, there were 13 cases of CIN, with an incidence of 8.9%, there was no statistically significant difference between the two groups (P＞0.05). Statistically difference was found in gender and perioperative use of ACEI/ARB between two groups (P<0.05). Preoperation BNP, fibrinogen, platelet volume distribution of the diabetes group was higher than non-diabetic, 25 hydroxyvitamin D was lower than non-diabetic group (P<0.05). Loistic regression analysis showed that fibrinogen and 25 hydroxyvitamin D were the risk factors of CIN for elderly diabetic patients with acute coronary syndrome after PCI. Preoperative fibrinogen elevation increased the risk of CIN (OR=3.3,5%CI 1.353～6.845, P=0.007), 25 hydroxyvitamin D reduction increased the risk of CIN (OR=0.5,5%CI 0.282～0.833, P=0.009). Conclusion The risk of CIN was increased when preoperative fibrin was elevated and 25 hydroxyvitamin D was decreased in elderly diabetes mellitus patients with acute coronary syndrome after PCI.