Introduction: Graft-versus-host disease (GVHD) is the most common complication of hematopoietic stem cell transplantation (HSCT); therefore, the prevention of GVHD is important for a successful treatment. Tacrolimus (Tac), a calcineurin inhibitor, has been widely used for the prophylaxis of GVHD in HSCT recipients. Areas covered: This review introduces phase II/III of clinical trials related with Tac's roles in the prevention of GVHD in HSCT. Furthermore, we discuss the normal ranges of Tac concentrations, pharmacogenetics, and drug interactions of Tac, as well as its side effects in adult HSCT recipients. Expert opinion: A series of studies has established the efficacy and safety of Tac alone or in combination with other agents in HSCT. However, successful administration of Tac is complicated by its narrow therapeutic window, inter-patient pharmacokinetic variability, and a spectrum of undesirable side effects. It is necessary to maintain concentrations of Tac within the desired ranges for GVHD prophylaxis. Moreover, various factors contribute to significant variability in Tac pharmacokinetics, including drug interactions and genomic variation.