Background: Feeding intolerance (FI) is a common clinical problem in preterm infants often caused by some neonatal disorders and drugs, including antenatal exposure to magnesium sulfate (MgSO 4 ).Objective: To evaluate the association between hypermagnesemia at birth and FI in preterm infants during the first 72 h of life.Method: This was a cohort study conducted with preterm infants aged <34 weeks' gestation. Infants presenting at least two of the following signs were considered as having FI: vomiting, abdominal distension, the need for continuous intermittent feeding, and delayed meconium passage. Hypermagnesemia was characterized by umbilical serum Mg levels > 2.5 mEq/L.Results: A total 251 infants were evaluated. The median birth weight and gestational age were 1390 g (IQR, 1020-1070) and 31 weeks (IQR,(28)(29)(30)(31)(32). The FI rate was 17.5%. The exposure rate to MgSO 4 was similar in the tolerant and intolerant groups (53.1% × 63.6%; P = 0.204), but hypermagnesemia was more frequent in the FI group (40.9% × 24.2%; P = 0.024). The univariate analysis showed that infants with hypermagnesemia were twofold more likely to present FI (odds ratio [OR], 2.16; 95% CI, 1.09-4.26). In the multiple logistic regression analysis, we found that hypermagnesemia was independently associated with FI (OR, 2.51; 95% CI, 1.06-5.91), as well as maternal diabetes mellitus