It is known that Immunosuppression post-Liver transplant is central to achieving optimal outcomes in liver transplant recipients. It is required to maintain an adequate balance between reducing rejection and toxicities. Mainstay drugs for maintenance therapy are Calcinuerin inhibitors - Tacrolimus versus cyclosporine. Tacrolimus is preferred, as it has less rejection and better graft survival. However, there is risk of renal and metabolic toxicities. Tacrolimus is bound mainly to alpha1-acid-glycoprotein (encoded by the ABCB1gene) expressed on various epithelial and endothelial cells and lymphocytes. Elimination occurs by metabolizing enzymes of cytochrome P450 system, with biliary excretion (95%) of metabolites (majority) with minority through urine (2.4%). Demethylation and hydroxylation of tacrolimus occurs by hepatic and intestinal CYP3A isoforms (CYP3A4 and CYP3A5). Among the factors that play an important role in the pharmacokinetics of tacrolimus, thus affecting the tacrolimus trough levels in the body and in turn influencing the dosing of the drug required to maintain an adequate balance between reducing rejection and toxicities, genetics plays an important role. Increased expression of CYP3A5 causes more metabolism of tacrolimus and hence affecting the tacrolimus concentration/weight-adjusted dose (C/W-D) ratio in the body. The wild type (CYP3A5\*3) are slow metabolizers and mutant ones (CYP3A5 \*1/\*1 and CYP3A5 \*1/\*3) are fast metabolizers. Fast metabolizers have a low C/W-D ratio and require higher Tacrolimus dosing and are thus susceptible to renal and metabolic toxicities, EBV viremia and post transplant lymphoproliferative disorder. Polymorphisms in ABCB1 (c.3435C\>T) are also known to influence tacrolimus dosage in the first week of transplant (C/D ratio was lower in ABCB1 3435CC in comparison to CT and TT). There is no such data in pediatric liver transplant setting from Indian subcontinent. The aim of the study is to study the prevalence of CYP3A5 polymorphisms in the donors and ABCB1 polymorphisms in the recipients undergoing Paediatric liver transplant and their influence on Tacrolimus levels and graft function.