Aim: We evaluated whether nasal high-flow therapy was better than no respiratory support during the weaning phase in preterm infants.Methods: The study was conducted in the neonatal intensive care unit of the Turku University Hospital between September 2014 and August 2015. Preterm infants who were alternating between nasal high-flow therapy and unassisted breathing were enrolled. Electrical activity of the diaphragm (EAdi) was recorded and compared during three-hour time periods for each option.Results: We studied eight infants at a median gestational age of 31 weeks. The EAdi peak was lower during nasal high-flow therapy when compared to no respiratory support (6.1 mV vs 7.1 mV, p = 0.02), but the EAdi minimum was similar with and without respiratory support. Neural respiratory rate (62 vs 68 per minute, p = 0.02) and the frequency of sighs (27.8 vs 37.9 per hour, p = 0.03) were lower during nasal high-flow therapy than no respiratory support.Conclusion: Nasal high-flow therapy reduced diaphragm activation in our cohort when compared to no respiratory support, as indicated by the lower Edi peak. An increase in the respiratory rate and the sigh frequency without respiratory support also suggests that nasalhigh-flow therapy provided support during the weaning phase.