Progression to non-alcoholic steatohepatitis (NASH) manifests as hepatitis, fibrosis, and sometimes carcinoma, resulting in liver failure. Various clinical trials have indicated that several pharmacological agents, including angiotensin II receptor blockers (ARBs) or farnesoid X receptor (FXR) agonists, are effective in NASH treatment. In addition, functional foods are expected to be important alternatives for treating or preventing NASH. Recently, focus has been directed toward microalgae as dietary supplements, mainly for lifestyle-related diseases, because they contain various nutrients and functional ingredients. Specifically, a unicellular microalga stores a unique β-1,3-glucan particle called paramylon that stimulates the immune system. In this study, we evaluated the effects of and paramylon on NASH in Stelic Animal Model (STAM) mice using Sirius red staining and confirmed that oral administration of or paramylon inhibits the process of liver fibrosis. Moreover, compared with controls, paramylon decreased non-alcoholic fatty liver disease (NAFLD) activity scores related to inflammation. These results indicate that the oral administration of and paramylon inhibits fibrosis and ameliorates NASH.