Aim: Pulmonary near-infrared spectroscopy (NIRS) is a new and promising tool for diagnosis of neonatal respiratory diseases (RD). The study aimed to determine the role of pulmonary regional oxygen saturation (pRSO ₂) values obtained by NIRS in the early distinction of neonatal pneumonia (NP) from transient tachypnea of the newborn (TTN). Methods: This prospective, observational, double-blind study was conducted in neonatal intensive care unit (NICU) between 2020-2021. Late preterm and term newborns hospitalized in the NICU due to the diagnosis of TTN and NP were included. Cerebral RSO2 and pRSO2 values were measured during the 1 ^st, 24 ^th, 48 ^th and 72 ^nd hours of hospitalization, using NIRS. Results: Of the eligible 40 infants, 65% (n:26) were diagnosed as TTN and 35% (n:16) as NP. The pRSO ₂ values were significantly higher in the TTN group than the NP group for both apexes (75.3±8.7 vs. 69±5.4, p:0,018, respectively) and lateral lung (77.8±6 vs. 72.7±6.2, p:0,016, respectively) in the 1 ^st hour of hospitalization. There were significant differences in pRSO ₂apex and pRSO ₂lateral values between the 1 ^st and 24 ^th hours of hospitalization and the 24 ^th and 48 ^th hours in the NP group (p ²: 0.001 for both). The optimal pRSO ₂apex cut-off value was >72% to predict the diagnosis of NP with a sensitivity of 78.6% and a specificity of 69.2%. Conclusion: Pulmonary NIRS may be considered as a feasible and promising diagnostic tool in late preterm and term infants with RD. It may also be helpful for the early differentiation of NP from TTN and the courses of these diseases.