The present invention relates to a composition or cell therapeutic agent for preventing or treating liver fibrosis, containing an exosome or exosome-derived ribonucleic acid. The exosome or ribonucleic acid derived therefrom, of the present invention, has effects of inhibiting activities of hepatic stellate cells and Kupffer cells and reducing the expression of α-SMA and inhibits the progression of liver fibrosis by inhibiting the deposition of collagen, thereby being effectively usable as a cell therapeutic agent for the prevention or treatment of liver fibrosis.