To describe breastfeeding-supportive practices in U.S. maternity hospitals with advanced neonatal care units (ANCU). Using 2022 mPINC data, we calculated the percent of hospitals reporting (1) breastfeeding-supportive practices for "most" (≥80%) mother-baby dyads in ANCUs, by hospital demographic characteristics and (2) infant receipt of mother's own milk or donor milk at any time while in the ANCU, by ANCU level. More than 90% of hospitals reported that "most" mothers (≥80%) were advised on some breastfeeding-supportive practices. Fewer hospitals reported that "most" mothers expressed milk within one hour of birth (37%) or that kangaroo care was practiced for "most" eligible newborns (63%). Receipt of mother's own milk varied by unit level and state. Breastfeeding-supportive practices requiring the technical competency of healthcare providers (e.g., early milk expression, kangaroo care) are less likely to be implemented in ANCU settings compared to practices centered around providing advice or education.