Background and Objectives: Kangaroo mother care (KMC) benefits preterm infants' health through increasing breastfeeding, but the longitudinal effects of KMC remain unknown. This study investigates the impact of KMC on breastfeeding and health outcomes in Chinese preterm infants. Methods: A longitudinal randomized controlled study was conducted with 79 preterm infant-mother dyads. The KMC group (n = 36) was provided 2.5 hours/day KMC during the neonatal intensive care unit (NICU) hospitalization, while the control group (n = 43) received standard care. Infant's feeding regimens and physical growth were documented daily at NICU. Physical growth and Neonatal Behavioral Neurological Assessment were measured at 40 weeks, 3 months, and 6 months of corrected age (CA). Breastfeeding outcomes were documented at 6 months of CA. Results: Compared with the control group, KMC infants received higher mothers' milk proportion during hospitalization (B = 0.16, confidence interval [CI] = [0.11-0.21]) and less feeding intolerance at discharge (odds ratio [OR] = 0.11, CI = [0.02-0.43]); and higher exclusive breastfeeding proportion (OR = 14.6, CI = [3.5-60.9]) at 6 months CA. KMC infants also had significant increased body weight and body length at hospital discharge; and more increases of body weight, body length, and head circumference in follow-ups. The neurobehavioral score was also higher in the KMC group compared to the control group over time. Conclusions: Longitudinal KMC effects are significant in promoting preterm infants' breastfeeding outcomes, growth, and neurodevelopment. Early initiation of KMC practice is highly recommended to the parent-infant population in Chinese NICUs to promote breastfeeding and developmental outcomes.