Recently, the diagnostic criteria for idiopathic cerebellar ataxia (IDCA) have been proposed in Japan as a diagnosis to replace the clinical concept of cortical cerebellar atrophy, which was originally described as a neuropathological disorder. However, IDCA proposed in Japan may include various diseases such as multiple system atrophy with early stage, rare hereditary ataxias, and autoimmune-mediated cerebellar ataxia. We tackled this significant clinical challenge by detecting anti-cerebellar autoantibodies in patients' sera and identifying their target antigens. We detected anti-cerebellar autoantibodies in the sera of some patients diagnosed with IDCA in Japan. In the future, it will be necessary to confirm the efficacy of immunotherapy for anti-cerebellar autoantibody-positive cases among patients who were thought to be difficult to treat.