Currently, there are no approved treatments for infants with acute bronchiolitis, the leading cause for hospitalization of infants worldwide, and thus the recommended approach is supportive. Inhaled Nitric oxide (iNO), possesses anti-viral properties, improves oxygenation, and was shown to be safe in infants with respiratory conditions. Hospitalized infants with acute bronchiolitis were therefore recruited to a prospective double-blinded, multi-center, randomized controlled pilot study. They received intermittent high dose iNO (160 ppm) plus oxygen/air for 30 min or oxygen/air alone (control), five times/day, up to 5 days. Sixty-nine infants were enrolled. No difference was observed in frequencies of subjects with at least one Adverse Event (AE) in iNO (44.1%) vs. control (55.9%); neither was Methemoglobin >7% safety threshold. No drug-related serious AEs (SAEs) were reported. Analysis of Per-Protocol population revealed that length of stay (LOS), time to SpO2 ≥92%, and time to mTal clinical score ≤5 improved by 26.7 ± 12.7 (Welch's t-test p = 0.04), 20.8 ± 8.9 (p = 0.023), and 14.6 ± 9.1 (p = 0.118) hours, respectively, in the iNO group compared to the control. Overall, high dose iNO (160ppm) was safe, well-tolerated, reduced LOS and showed rapid improvement of oxygen saturation, compared to the standard therapy. Further investigation in larger cohorts is warranted to validate these encouraging efficacy outcomes. (Trial registration: NCT03053388).