Abstract: OBJECTIVE To study the reasons of abnormal tacrolimus concentration on organ transplant. METHODSTacrolimus concentration in blood was determinated and date of concentration was analyzed according to clinical experience of American university of pittsburgh. RESULTSThere were 1 296 cases(66.6%) in normal range group,382 cases(19.6%) below minimum group and 269 cases(13.8%) over maximum group.CONCLUSIONThere are many reasons which can fluctuate drug.We must provided reasonable explanation on results, what can help individual adminstration.