Aim To investigate the association between the fibrinogen/albumin ratio (FAR) and the severity of coronary artery disease in unstable angina (UA) patients. Methods Retrospective analysis was performed on 140 UA patients. According to the receiver operating characteristic(ROC) curve, patients were divided into two sub-groups based on the best critical value of FAR to predict moderate to severe coronary artery disease(Gensini score>20 scores). The clinical data, laboratory test results and coronary artery diseases of the two groups were compared. Multivariate Logistic regression analysis was used to study the related risk factors of moderate to severe coronary artery disease in UA. Results The best critical value of FAR value to predict moderate to severe coronary artery lesions in UA patients was 0.068 8, when the area under the curve was 0.705 (95%CI:0.613~0.797), the sensitivity was 74.0% and the specificity was 60.0%. There were significant differences in diabetes and smoking history between the two groups (both P＜0.05); The white blood cell count, low density lipoprotein cholesterol, total cholesterol, fasting blood glucose and fibrinogen were higher in the high FAR group than those in the low FAR group, while the levels of high density lipoprotein cholesterol and albumin were lower than those in the low FAR group(all P＜0.05); With the increase of the FAR ratio, the vascular lesions in the single branch gradually decreased, and the vascular lesions in the two and three branches and the Gensini score gradually increased. The differences were statistically significant (all P＜0.05). Spearman correlation analysis indicated that FAR was positively correlated with Gensini score (r＝0.606, P＜0.001). Multivariate Logistic regression showed that FAR≥0.068 8(OR＝7.553, P＝0.016) was an independent risk factor for moderate to severe coronary artery disease in UA patients. Conclusion In UA patients, the FAR value≥0.068 8 has certain value in predicting the severity of coronary artery diseases.