Introduction. The rapid antigen test (RAT) plays an important role in the Emergency Room (ER). In this study, we investigated the effect of the RAT for influenza on clinical practice in an emergency department.Methods. A retrospective chart review was conducted considering two periods, namely before and after the 2009 influenza pandemic. The rate of antibiotic administration, the use of blood sample tests, the use of simple chest X-rays, the rate of antibiotic administration according to the result of the RAT, and the duration of ER stay in the case of influenza-like illnesses were investigated for the two study periods considered.Results. The use of the RAT increased from 23.9% to 39.8% in influenza-like pediatric patients (p<0.05) and from 4.9% to 67.6% in adult patients (p<0.001). After the 2009 influenza pandemic, the number of cases of antibiotic administration, blood sample test and simple chest X-ray decreased by 19.0%, 46.2%, and 27.4%, respectively, in pediatric patients with the use of RAT. Among RAT-positive patients, after the 2009 influenza pandemic, none of the pediatric patients and only 3 of the adult patients (17.6%) were administered antibiotics. The duration of ER stay was longer in patients who underwent RAT than in those who did not.Conclusion. The increased use of RAT for influenza has led to a decrease in antibiotic administration and a reduction in additional diagnostic tests in influenza-like illnesses. However, the use of RAT has not contributed to a decrease in the duration of ER stay.