MicroRNAs (miRNAs) are a large family of non-coding RNAs that are evolutionarily conserved, endogenous, and 21-23 nucleotides in length. miRNAs regulate gene expression by targeting messenger RNAs (mRNAs) by binding to complementary regions of transcripts to repress their translation or mRNA degradation. miRNAs are encoded by the genome, and more than 1000 human miRNAs have been identified so far. miRNAs are predicted to target ∼60% of human mRNAs and are expressed in all animal cells and have fundamental roles in cellular responses to xenobiotic stresses, which affect a large range of physiological processes such as development, immune responses, metabolism, tumor formation as well as toxicological outcomes. Recently, many reports concerning miRNAs related to cancer have been published; however, the miRNA research in the metabolism of xenobiotics and endobiotics and in toxicology has only recently been established. This review describes the current knowledge on the miRNA-dependent regulation of drug-metabolizing enzymes and nuclear receptors and its potential toxicological implications. In this review, miRNAs with reference to target prediction, potential modulation of toxicology-related changes of miRNA expression, role of miRNA in immune-mediated drug-induced liver injury, miRNA in plasma as potential toxicological biomarkers, and relevance of miRNA-related genetic polymorphisms are discussed.