Objective: Arterial blood gas analysis (ABGA) is routinely performed in hyperventilation syndrome (HVS) patients in the emergency department (ED). We tried to substitute end-tidal carbon dioxide (ETCO2) for arterial partial pressure of carbon dioxide (PaCO2) in HVS patients in ED. Methods: It was a prospective observational cohort study of HVS patients from May 2019 to March 2020. Data of age, sex, vital sign, ETCO2 and ABGA were collected. We compared the Pearson correlation between ETCO2 and PaCO2. Results: A total of 135 HVS patients were included in the study. The average value for ETCO2 was 24.9±7.2. It showed a significant linear between ETCO2 and PaCO2. The Pearson correlation coefficient was 0.893 (P<0.001). The linear correlation coefficients of ETCO2 <20 mmHg and ETCO2 20-35 mmHg groups were 0.513 and 0.827, respectively (P<0.001). Conclusion We suggest that ABGA can be replaced by ETCO2 in HVS patients in ED.