MicroRNAs (miRNAs) have a role in the cellular defense mechanism. Nuclear factor erythroid-2-related factor 2 (Nrf2) increases antioxidant enzyme capacity. However, miRNA transcriptionally controlled by Nrf2 had been uncharacterized. Here we report that miR-125b is transactivated by Nrf2 and inhibits aryl hydrocarbon receptor (AhR) repressor (AhRR). Bioinformatic approaches enabled us to extract six candidate miRNAs. Of them, only miR-125b was increased in the kidney of mice treated with oltipraz. Nrf2 overexpression enhanced primary, precursor and mature miR-125b levels. Functional assays revealed MIR125B1 is a bona fide target gene of Nrf2. Oltipraz treatment protected the kidney from cisplatin toxicity with increase of miR-125b. Consistently, Nrf2 knockout abrogated an adaptive increase of miR-125b elicited by cisplatin, augmenting kidney injury. An integrative network of miRNA and messenger RNA changes enabled us to predict miR-125b as an inhibitor of AhRR for the control of AhR activity and cell survival. In our molecular study, miR-125b inhibited AhRR and thereby activated AhR, leading to the induction of mdm2. Consistently, p53 activation by cisplatin was diminished by either miR-125b or oltipraz treatment. The results of experiments using miR-125b mimic or small interfering RNA of AhRR verified the role of miR-125b in AhRR regulation for kidney protection. In conclusion, miR-125b is transcriptionally activated by Nrf2 and serves as an inhibitor of AhRR, which contributes to protecting kidney from acute injury.