Objectives: This study sought to evaluate the relative efficacy of expressed breast milk (EBM) fortified using human milk fortifier (HMF) compared to commercial preterm formula (PF) on preterm and very low birth weight (VLBW) infants in a major tertiary healthcare center in Oman. Methods: This retrospective cohort study included two cohorts of preterm (< 32 weeks gestation) or VLBW infants (birth weight < 1500 g) treated in the neonatal intensive care unit (NICU). Cohort one included infants who were given PF-fortified EBM between January and December 2016, and cohort two were given newly-introduced HMF-fortified EBM between November 2018 and December 2019. Analysis was performed to compare the cohorts with respect to baseline characteristics, primary outcomes, and secondary outcomes. Results: A total of 103 neonates were included (cohort 1: n = 55, cohort 2: n = 48). There were no significant differences in the growth of the weekly length, the growth of the head circumference, or discharge growth parameters. Compared to PF, HMF was associated with significantly better weight gain velocity (g/kg/day) during the first week (p =0.009) and second week (p =0.050) after starting fortification, lower need for other adjunctive forms of fortification (p =0.035), and lower rates of necrotizing enterocolitis in premature infants or VLBW (p =0.018). Conclusions: This is likely to be the first study to analyze the relative efficacy of HMF and PF in the Middle East. The results of this study will be helpful in guiding standards of nutritional care in NICUs in Oman.