Objective：This study aims 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 100.0%，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 93.0%，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.