Objective: To evaluate the diagnostic value of peripheral blood circ_0070934/miR-199a-5p/MGAT3 in combined allergic rhinitis and asthma syndrome (CARAS).Methods: Peripheral venous blood was collected from 38 CARAS patients and 43 healthy controls. Plasma MGAT3 protein level was detected by ELISA, and the expression level of circ_0070934/miR-199a-5p/MGAT3 in peripheral blood was detected by quantitative real-time PCR (qRT-PCR). Diagnostic sensitivity and specificity were determined by ROC curve. Results: ELISA results showed that MGAT3 concentration in CARAS patients was significantly lower than that in control group (P=0.035). The circ_0070934 (P=0.001) and MGAT3 mRNA expressions (P<0.001) in CARAS patients were down-regulated when compared with control group, while miR-199a-5p was up-regulated (P=0.013). Correlation analysis showed that MGAT3 was positively correlated with the count of eosinophils and the percentage of eosinophils, while circ_0070934 showed a negative correlation. ROC curve analysis indicated that MGAT3 was the best parameter. When the cut-off value was 0.208, the sensitivity and specificity were 73.7% and 100%, respectively, and the AUC was 0.933 (95%CI=0.882-0.984, P<0.001). The combination of circ_0070934, miR-199a-5p and MGAT3 had the highest diagnostic value for CARAS. When the cut-off value was 0.539, the sensitivity was 92.1%, the specificity was 93%, and the AUC was 0.959 (95%CI=0.916-1.000, P<0.001).Conclusion: Altered expressions of circ_0070934/miR-199a-5p/MGAT3 were confirmed in the peripheral blood of CARAS patients, which can be used as a biomarker for the diagnosis of CARAS. Further researches on the specific role and mechanism of circ_0070934/miR-199a-5p/MGAT3 in CARAS will help to discover new diagnostic and therapeutic targets of CARAS.