The present disclosure relates to a pharmaceutical composition for preventing or treating a brain disease, more particularly to a pharmaceutical composition for preventing or treating a brain disease, which contains a miR-485-3p inhibitor, and a method for screening an agent for preventing or treating a brain disease, which includes a step of measuring the expression level of miR-485-3p. Because the composition for treating a brain disease, which contains a miR-485-3p inhibitor, can restore the ELAVL2 protein unlike the exiting therapeutic agents for Alzheimer's disease, which are limited only to alleviating symptoms by inducing decreased expression of amyloid beta 42, the present disclosure can fundamentally treat various diseases caused by decreased expression of ELAVL2, such as Alzheimer's disease, autism spectrum disorder, mental retardation, amyotrophic lateral sclerosis, etc. Therefore, the present disclosure is useful for treating brain diseases including Alzheimer's disease fundamentally.