Background: Acute bronchiolitis is the inflammation of the bronchioles, which is most typically caused by a virus and is common in children under the age of two. The aim of this study was to evaluate if serum albumin levels on admission are associated with severity of illness in infants with Acute bronchiolitis according to their Modified Tal score. Methods: This single-center, case control observational study included 50 infants with acute bronchiolitis and 50 healthy infants as a control group. All cases were subjected to full history taking, complete clinical examination, modified Tal score and laboratory investigations as complete blood count, arterial blood gases, C reactive protein and serum albumin level. Results: Bronchiolitis group included 26 females and 24 males; their mean age was 7.5±4.8 months. There was no statistical difference between cases and control regarding their age, sex, gestational age, nutritional history or age of weaning. Most cases (42%) had mild disease, 38% of cases had moderate disease and 20% of cases had severe disease. Bronchiolitis group had statistically higher serum albumin compared to control group. Cases with severe bronchiolitis had statistically lower albumin level compared with moderate and mild cases. Serum albumin could detect cases with acute bronchiolitis from controls; AUC was 0.724 (CI: 0.626-0.822), p < 0.001 and detect severe cases with acute bronchiolitis; AUC was 1, p < 0.001. Conclusion: Serum albumin levels can be an objective, inexpensive and widely available biomarker to use in conjunction with the current clinical scores to diagnose and to assess severity of the disease