Background and Objectives: Feeding intolerance (FI) is a common problem in late preterm infants (34 weeks ≤ gestational age < 37 weeks). This study aimed to evaluate the efficacy and safety of phentolamine combined with B vitamins in treating FI in late preterm infants and to explore its effects on gastrointestinal symptoms, inflammation and complications. Methods and Study Design: We randomly assigned 118 late preterm infants with FI to a treatment group (n = 56) or a control group (n = 62). The treatment group received intravenous phentolamine and intramuscular B vitamins, whereas the control group received basic treatment only. We measured the time of disappearance of gastrointestinal symptoms, the time of basal attainment, the time of hospitalisation, the incidence of complications, the concentrations of inflammatory markers and the overall effective rate of treatment. Results: The treatment group had a shorter duration of gastrointestinal symptoms than did the control group (p < 0.01). The treatment group also had lower concentrations of inflammatory markers and a higher overall effective rate than did the control group (p < 0.05). There was no difference between the two groups in the time of hospitalisation, basal attainment, weight recovery and the incidence of complications (p > 0.05). Conclusions: Phentolamine and B vitamins can reduce gastrointestinal symptoms and inflammation in late preterm infants with FI but do not affect the occurrence of complications.