Background: The aim of this study was to evaluate the efficacy and safety of early administration of Bifidobacterium bifidum OLB6378 (B. bifidum) on accelerating enteral feeding and bacterial colonization in very-low-birthweight (VLBW) infants. Methods: We conducted a single-center prospective pilot study. Thirty-six VLBW infants were randomly divided into two groups: group E, wherein B. bifidum was supplemented within 48 h of birth, and group L, wherein it was supplemented more than 48 h after birth. Results: Group E and group L reached a total feeding volume of 100 mL/(kg/day) after 10 [7–13] days and 11 [10–15] days, respectively (median [quartile]). The daily bodyweight gain in group E was significantly higher (21.4 ± 3.2 g/day vs 18.3 ± 4.0 g/day, P < 0.02; 11.1 ± 1.5 g/kg/day vs 10.4 ± 1.2 g/kg/day, P < 0.04). No significant differences were found in the fecal Bifidobacterium level between the groups quantitated with a real-time polymerase chain reaction assay at 1 and 4 weeks of age. However, the highest colonization rate of Bifidobacterium was observed when the supplementation started between 24 and 48 h after birth. The incidence of morbidities between the groups was similar. Conclusion: The early administration of B. bifidum to VLBW infants seems effective in promoting growth during the stay in the neonatal intensive care unit without increasing the incidence of morbidity. Furthermore, the preferable timing of starting the probiotic supplementation for VLBW infants is at latest less than 48 h after birth.