Objective We aimed to compare the heated humidified high‐flow nasal cannula (HHHFNC) flow rate of 1‐L·kg·min−1 (1 L) with 2‐L·kg·min −1 (2 L) in patients with severe bronchiolitis presenting to the pediatric emergency department. Study design We performed a study in which all patients were allocated to receive these two flow rates. The primary outcome was admitted as treatment failure, which was defined as a clinical escalation in respiratory status. Secondary outcomes covered a decrease of respiratory rate (RR), heart rate (HR), the clinical respiratory score (CRS), rise of peripheral capillary oxygen saturation (SpO2), and rates of weaning, intubation, and intensive care unit (ICU) admission. Results One hundred and sixty‐eight cases (88 received the 1‐L flow rate and 80, the 2‐L flow rate) were included in the analyses. Treatment failure was 11.4% (10 of 88) in the 1‐L group, and 10% (8 of 80) in the 2‐L group (P = .775). Significant variation in the intubation rate or the ICU admission rate was not determined. At the 2nd hour, the rate of weaning (53.4% vs 35%; P = .017), the falling down of the CRS (−2.1 vs −1.5; P < .001), RR (−15.2 vs −11.8; P < .001), and HR (− 24.8 vs − 21.2; P < .001), and the increase of SpO 2 (4.8 vs 3.6; P < .001) were significantly more evident in the 1‐L group. Conclusion HHHFNC with the 1‐L·kg·min−1 flow rate, which provides a more frequent earlier effect, reached therapy success as high as the 2‐L·kg·min −1 flow rate in patients with severe acute bronchiolitis.