Objectives Environmental stimuli in neonatal intensive care units can disrupt the physiological stability and sleep of infants. It is essential to perform nursing interventions to reduce the adverse effects of such stimuli. This study aimed to compare the effect of recorded lullabies and mothers’ live lullabies on physiological responses and sleep duration of preterm infants. Methods This study was a randomized clinical trial. The participants were 90 preterm infants selected using convenience sampling. In the intervention groups, music (recorded lullabies and mother’s live lullabies) was played for 14 days, 20 min a day, while the control group did not receive any intervention. The data were collected using physiological criteria and infant sleep checklists before, during, and after the intervention. The data were analyzed using SPSS software (Version 21.0). Results The mean scores of physiological parameters (O2 saturation and heart rate) were not significantly different in the three groups before, during, and after the intervention (p>0.05). However, there was an improvement in O2-saturation and a decrease in the heart rate in two intervention groups. The mean duration of the infants’ overnight sleep was not statistically significant between the groups before the intervention (p>0.05). However, there was a statistically significant difference in the intervention groups after the intervention, (p<0.05), and the infants’ overnight sleep was longer in the recorded-lullaby group than the other two groups. Conclusions Although performing interventions, including recorded lullaby and mother’s live lullaby did not differ significantly with that of the control group in physiological criteria, it can be clinically important. In addition, recorded-lullaby increased the infants’ overnight sleeping. Thus, it is suggested that further studies be conducted to confirm the effect of recorded lullaby and mother’s live lullaby interventions on physiological parameters and sleep duration of hospitalized infants.