In this study, the regulation of miR-15b-5p on myocardial ischemia reperfusion (I/R) injury-induced arrhythmia and myocardial apoptosis was investigated in mice. We observed the change in miR-15b5p expression after mice suffered from myocardial I/R injury and the change in myocardial injury, infarct size, apoptosis, tumor necrosis factor-alpha (TNF-alpha), interleukin-6 (IL-6), superoxide dismutase (SOD) and malondialdehyde (MDA) after down-regulation of miR-15b-5p expression. The negative regulation of miR-15b-5p to KCNJ2 as well as whether cardioprotective effect formed by miR-15b-5p down-regulation relied on the increase of KNCJ2 expression were measured by dual-luciferase reporter assay system. miR15b-5p expression increased and KCNJ2 mRNA and protein expressions decreased after myocardial ischemia reperfusion (all P < 0.05). miR-15b-5p negatively regulated KCNJ2 in a targeted way. Downregulating miR-15b-5p expression or increasing KCNJ2 expression significantly decreased the incidence of arrhythmia, infarct size and apoptosis after myocardial I/R and lowered MDA content in the myocardial tissue as well as IL-6 and TNF-alpha content in the blood (all P < 0.05). KCNJ2 gene knockout reversed the above cardioprotective effect formed by miR-15b-5p down-regulation (P < 0.05). Downregulating miR-15b-5p expression or up-regulating KCNJ2 expression improves arrhythmia after mice suffered from myocardial I/R injury and inhibits myocardial apoptosis. (C) 2020 Published by Elsevier Inc.