With the advent of Twenty-First century, more and more genome-wide association studies (GWAS) showed that idiosyncratic adverse drug reactions (ADRs) were closely related with human leukocyte antigen (HLA) alleles, such as the associations of abacavir-HLA-B5701, allopurinol-HLA-B5801, and carbamazepine-HLA-B*1502, etc. To explore the mechanisms of these idiosyncratic drug reactions, hapten hypothesis, danger signal hypothesis, pharmacological interaction (P-I) concept and autoimmune mechanism are proposed. In this paper, recent GWAS studies on the HLA-mediated adverse drug reactions and underlying mechanism are reviewed in detail.