Background: Gastro-oesophageal reflux (GOR) is common in preterm infants; conservative interventions (i.e. dietary changes) should represent the first-line approach. Aim: To evaluate by combined pH and impedance monitoring (pH-MII) the effect of a new preterm formula thickened with amylopectin (TPF) on GOR features in symptomatic preterm infants. Methods: Twenty-eight symptomatic preterm newborns underwent a 24-hour pH-MII; each baby received eight meals (four of TPF and four of a preterm formula [PF]). GOR indexes (number, acidity, duration and height of GORs) after TPF and PF meals were compared by Wilcoxon Signed Ranks Test. Viscosity of PF and TPF was measured. Results: TPF significantly decreased the number of acid GORs detected by pH-monitoring (TPF vs. PF: median 20 vs. 24.5, p = 0.009), while it had no influence on Reflux Index (RIpH), nor on acid and non-acid GOR indexes detected by MII, GOR physical features, and GOR height. TPF's viscosity was extremely higher than PF's, and further increased at pH 3 after the addition of pepsin. Conclusions: The new formula was found to reduce the number of acid GORs detected by pH-monitoring; it did not reduce neither total oesophageal acid exposure nor non-acid GORs. At present its extended clinical use cannot be recommended.