© 2020, International Pediatric Research Foundation, Inc. Background: To determine normative data by forced oscillation technique (FOT) in non-sedated normal term neonates and test the hypothesis that infants with transient tachypnea of the newborn (TTN) have higher resistance (R) and lower reactance (X) on day 1. Methods: Healthy term infants (n = 138) and infants with TTN (n = 17) were evaluated on postnatal days 1 through 3 (NCT03346343). FOT was measured with a mask using a TremoFlo C-100 Airwave System™. R, X, and area under the reactance curve (AX) were measured at prime frequencies 7–41 Hz for 8 s. Results: In all, 86% of control infants had adequate measurements (coherence >0.8, CV < 0.25) on day 1. Infants with TTN had higher resistance at 13 Hz (TTN 32.5 cm H2O·s/L [95% CI 25.5–39.4]; controls 23.8 cm H2O·s/L [95% CI 22.2 to 25.3], P = 0.007) and lower reactance from 17 to 37 Hz (TTN −35.1 to −10.5; controls −26.3 to −6.1, P < 0.05). In healthy controls, lung mechanics were unchanged from days 1 to 3. In TTN, lung mechanics normalized on days 2 and 3. Conclusions: FOT is feasible in neonates and distinguishes normal control infants from those with TTN on postnatal day 1. Oscillometry offers a non-invasive, longitudinal technique to assess lung mechanics in newborns.