A number of environmental toxicants affect our health through physical, biological or chemical mechanisms. There is growing evidence indicating that microRNA (miRNA) plays an important role in toxicogenomics, disease aetiology and the effect of toxicants. This article summarises recent findings on miRNAs associated with various toxicants and those targeted in the development of therapeutics. Environmental epigenetic studies have revealed the role of miRNAs in the regulation of gene activities induced by environmental changes after exposure to toxic substances. Toxicant-induced changes in miRNA expression have a potential to be informative markers in the evaluation of toxicant risks. miRNAs are now considered to be predictive biomarkers or indicators of tissue injury due to toxicant exposure; thus, miRNAs can also be utilised as therapeutic targets.