Summary Objective: While propranolol pharmacokinetics has been extensively studied in adults, this study reports the first evaluation of propranolol pharmacokinetics in term and preterm neonates. Methods: Propranolol concentrations were measured in four term and thirty-two preterm newborns treated with oral propranolol at the dose of 0.5 or 0.25 mg/kg every 6 hour by serial dried blood spots. Results: The levels of propranolol, although with high inter-individual variability, were proportional with the administered dose. Pharmacokinetic parameters evaluated at the steady state in newborns treated with 0.5 mg/kg/6h showed values of maximal (71.7 ± 29.8 ng/mL), minimal (42.2 ± 20.8 ng/mL) and average concentration (60.8 ± 25.0 ng/mL), time of maximal concentration (2.6 ± 0.9 h) and area under the time-concentration curve (364.7 ± 150.2 ng/mL/h) similar to those observed in adults. In both dosing groups, elimination half-life was significantly longer (14.9 ± 4.3 and 15.9 ± 6.1 h), and apparent total body clearance (27.2 ± 13.9 and 31.3 ± 13.3 mL/kg/min) lower than those reported in adults, suggesting a slower metabolism in newborns. No differences were observed between newborns with different gestational age or different sex. Conclusions: Neonates treated with propranolol exhibited drug concentrations proportional with the dose, with significant long half-life.