Adequate nutrition is fundamental to neonatal survival and short-term outcomes, but it also has long-term consequences on quality of life and neurologic development of preterm infants. Donkey milk has been suggested as a valid alternative for children allergic to cows’ milk proteins, due to its biochemical similarity to human milk; we, hence, hypothesized that donkey milk could be a suitable basis for developing an innovative human milk fortifier for feeding preterm infants. The aim of the current study was to extend the findings and to evaluate the neurodevelopmental outcomes at 18 months of corrected age of the infants enrolled in the clinical trial named “Fortilat”. Infants born ≤1500 g and <32 weeks of gestational age were randomized to receive either a combination of bovine milk-based multicomponent fortifier and protein supplement or a combination of a novel multicomponent fortifier and protein supplement derived from donkey milk. The followed fortification protocol was the same for the two groups and the two diets were designed to be isoproteic and isocaloric. All infants enrolled were included in a developmental assessment program. The neurodevelopmental assessment was performed at 18 ± 6 months of corrected age. Minor and major neurodevelopmental impairment and General Quotient (GQ) at the Griffiths-II Mental Development Scale were considered. The GQ was considered both in continuous and as two classes: lower than and higher than (or equal to) a defined cutoff (GQcl). The difference in GQ and GQcl between the two arms was estimated using Mann–Whitney–Wilcoxon test or Fischer exact test, respectively, on the assumption of casual loss at follow-up. A further analysis was performed using generalized linear models. There were 103 children (bovine milk-derived fortifier arm = 54, donkey milk-derived fortifier arm = 49) included for the neurodevelopmental follow-up. All observations were included in the interval of 18 ± 6 months of corrected age. No significant difference was observed between the two arms in the incidence of neurologic sequelae and the GQs were similar in the two arms. Our results demonstrated no difference for the donkey milk-derived fortifier compared to standard bovine-derived fortifier regarding long-term neurodevelopmental outcomes.