Background Dyslipidemia is one of the most important factors for CAD. Atherogenic index of plasma (AIP) is a new indicator involved in dyslipidemia. However, its relation with CAD severity in diabetic patients is not well established yet. Aim of the Study To study the relationship between atherogenic index of plasma and severity of coronary artery disease (CAD) in the diabetic patients. Methods Our study was conducted on 150 diabetic patient with stable CAD undergoing elective coronary angiography in Al-Agoza Hospital from april 2016 to august 2018. Atherogenic index was calculated from the logarithmically transformed ratio of concentrations of TGs to HDL-C obtained from the patient’s lipid profile. correlation of the AIP and the severity of CAD according to Gensini scoring system was done. Results AIP had a statistically significant positive relation with IDDM (p = 0.033), NIDDM (p = 0.033), HTN (p = 0.024), dyslipedemia (p = 0.042). And a highly significant positive correlation with FBS (p < 0.001, r = 0.479) and HbA1c (p < 0.001, r = 0.538), proximal LAD lesions (p = 0.002), LCX (p < 0.001), and the number of vessls affected (p = 0.005). AIP Also had a highly significant positive correlation with severity of CAD in terms of Gensini score (p < 0.001, r = 0.692). Conclusion AIP is considered a good predictor of CAD severity and multivessel affection in diabetic patients.