Background: Respiratory failure is the common cause leading to life-threatening in children with pneumonia. The classification of respiratory failure with hypoxemia and/or hypereapnia plays an important role in the management of respiratory failure. Aim: To determine the rate of hypereapnia and some factors relating to hypereapnia in children with respiratory failure due to pneumonia at the National Children's Hospital. Subject and method: A prospective, cross-sectional descriptive study of 157 patients with respiratory failure due to pneumonia (from 2 months to 5 years old) hospitalized at the National Children's Hospital between 01/01/2017 to 30/09/2017. Result: Hypereapnia was accounted for 38.9% of patients with respiratory failure due to pneumonia, This proportion of the under i-year-old group (43.7%) was higher than the 1-5-year-old group (19.4%). The higher percentage was found in the wheezing group (49.2%) as comparing to the nonwheezing group (32.7%). There is no statistical significant difference in the ratio of hypereapnia in the preterm and full term children, in the groups diat had reduction of breath sound and atelectasis, emphysema in X-ray, as comparing to the non these symptoms groups. Conclusion: Hypereapnia is common in children with respiratory failure due to pneumonia, especially in the under 1-year-old group. Besides oxygen therapy, removing CO2 is necessary.Xác định tỷ lệ tăng CO2 và một số yếu tố liên quan đến tăng CO2 trên 157 trẻ suy hô hấp do viên phổi tại Bệnh viện Nhi Trung ương. Kết quả cho thấy tỷ lệ tăng CO2 gặp ở 38,9% trường hợp suy hô hấp do viêm phổi. Tỷ lệ tăng CO2 không có sự khác biệt ở nhóm trẻ có tiền sử đẻ non, nghe phổi giảm thông khí hoặc có tổn thương xẹp phổi, ứ khí trên Xquang sọ với nhóm trẻ không có những yếu tố này.