INTRODUCTION Functional and biochemical maturation of the gastrointestinal tract are established over the last trimester of gestation, which affects the digestive absorptive function of very preterm infants. Fecal calprotectin (FCP) indicates neutrophil migration to the gastrointestinal mucosa and can suggest the severity of mucosal inflammation. We investigated the fecal calprotectin level according to feeding kinds in very preterm infants with or without feeding intolerance (FI). PATIENTS & METHODS We prospectively investigated 68 very preterm infants born at 28-31 weeks’ gestation in Keimyung Universitiy Dongsan Medical Center between July 2016 and April 2017. All enrolled infants was fed within 3 hours of life using preterm formula, who achieved full enteral feeding (＞100cc/kg/day) within 7days of life. Fecal calprotectin levels were routinely investigated at 7days and 28days of life in fully enteral-fed very preterm infants without parenteral nutrition. FI was defined as gastric residual volume ≥ 50% of previous feeding volume, abdominal distention or emesis, and the disruption of the patient’s feeding plan. The infants with FI were temporarily fed with amino-acid based formula (AAF, Neocate®) after investigation with FCP. Infants with necrotizing enterocolitis, bacterial sepsis, and perinatal asphyxia during hospitalization were not included. FCP were measured by using a commercial quantitative enzyme-linked immunosorbent assay on the Alegria system (ORGENTEC Diagnostika, Mainz, Germany). RESULTS Median gestational age was 30.1 weeks, and median birth weight was 1488 g. The median age to achieve full enteral feeding was 3.8 days. In sixteen infants with FI, which was developed at median 3.3 days of life (range: 2-6 days of life), FCP levels in formula-fed or breast-fed infants (905±133 μg/g) was significantly higher than that in infants fed amino acid based-formula (217±232 μg/g) (p0.01). FCP level in formula-fed or breast-fed infants with FI (905±133 μg/g) was significantly higher than that without FI (405±267 μg/g) (p0.01). In infants without FI, FCP level in formula-fed infants (360±283 μg/g) was not significantly different with that in breast-fed infants (477±234 μg/g) (p＞0.05). CONCLUSIONS FCP might be sensitive according to feeding kinds in very preterm infants.