Purpose: To explore the benefits of a recorded maternal voice intervention on weight, recumbent length, head circumference, and heart rate of preterm infants in the neonatal intensive care unit. Methods: A pilot randomised controlled trial was conducted in this study. Preterm infants in the neonatal intensive care unit (N = 109) were recruited and randomly assigned to an intervention or control group. Both groups received routine nursing care, while preterm infants in the intervention group received a recorded maternal voice program of 20 min, twice daily for 21 days. Preterm infants' daily weight, recumbent length, head circumference, and heart rate were collected during the 21-day intervention. Participants' heart rate in the intervention group was also recorded once a day pre-during-after the recorded maternal voice program. Results: Preterm infants in the intervention group showed a significant increase in weight (−75.94, 95% CI −108.04, −43.85, P < 0.001), recumbent length (−0.54, 95% CI −0.76, −0.32, P < 0.001), and head circumference (−0.37, 95%CI −0.56, −0.18, P < 0.001) compared with the control group. Preterm infants in the intervention group also showed significant changes in heart rate pre-during-after the recorded maternal voice program. However, no significant differences were found in the heart rate scores between the two groups. Discussion: The changes in heart rate pre-during-after the intervention may help explain participants' more significant increase in weight, recumbent length, and head circumference. Practice implications: The recorded maternal voice intervention could be incorporated into clinical practice to promote growth and development in preterm infants in the neonatal intensive care unit. Study registration: Australian New Zealand Clinical Trials Register, https://www.anzctr.org.au/; (registration number: ACTRN12622000019707).