Anti-Homer-3 antibody associated cerebellar ataxia is a rare autoimmune cerebellar ataxia, which had been previously reported in 2 cases only. Here we present the third case where a middle-aged female experienced progressive cerebellar ataxia. A novel cerebellar ataxia antibody panel indicated sera of the patient was positive for anti-Homer-3 antibodies and established the diagnosis. Given steroids and long-term mycophenolate mofetil, the patient experienced partial improvement and remained stable in the follow-ups. Our report indicated immune-mediated causes should be considered in the context of 'idiopathic' cerebellar ataxia and immunotherapy could have therapeutic effects.