Purpose: This study examined the effects of upright nesting compared with swaddling on physiological status, sleep duration, and feeding tolerance in preterm infants in the neonatal intensive care unit. Methods: A total of 48 preterm infants, 24 per group, with gestational ages of 31 to 36 weeks, were enrolled. During the study, all infants were fed every 2 hours and did not receive sedation. Those requiring respiratory support or presenting with congenital abnormalities were excluded. At the unit level, participants were assigned to the “upright nesting” or the “swaddling” group. Physiological parameters, such as body temperature, oxygen saturation, heart rate, and respiratory rate, as well as sleep duration and feeding tolerance, were measured over 3 consecutive days. To examine group effects, time effects, and group-by-time interactions, linear mixed models were applied. Results: Baseline characteristics, including sex, birth weight, and gestational age, were comparable between groups. Infants receiving upright nesting showed higher mean body temperature and oxygen saturation, lower heart rate, longer sleep duration, and improved feeding tolerance. Linear mixed models presented significant main effects of time for temperature, oxygen saturation, and heart rate, while significant group effects were presented for sleep duration and feeding tolerance. Group by time interactions were not statistically significant, suggesting favorable trends without differential change over time. Conclusion Upright nesting supports physiological stability, promotes longer sleep duration, and enhances feeding tolerance in preterm infants. Furthermore, it is a promising supportive strategy in neonatal intensive care, but larger studies are needed to confirm the results.