The present invention relates to use of miR-18b for prevention, treatment, or diagnosis of muscle diseases or neuromuscular diseases, and specifically it was confirmed that, in a muscle disease by gene mutations model, gene mutations reduce miR-18b expression, cause dysregulation of miR-18b signaling pathways, and thus induce calcium signaling, cell differentiation inhibition, and apoptosis. Therefore, miR-18b of the present invention may be used as a target factor for diagnosing and treating muscle diseases caused by gene mutations such as ALS and DMD.