A case of paraneoplastic cerebellar ataxia syndrome caused by immune checkpoint inhibitors(ICI)was treated with ofatumumab(OFA).The patient is a 57-year-old male.He used"Camrelizumab"immunotherapy for his previous history of small cell lung cancer.The main reason was"walking unsteadily for more than one year and shaking his head involuntarily for more than one month".After admission,the head MRI,chest CT,electroencephalogram,lumbar puncture and other related examinations were improved.The antibody spectrum of paraneoplastic neurological syndrome was anti-GAD65 antibody IgG(+),and the case was then diagnosed as the immune checkpoint inhibitor-related paraneoplastic neurological syndromes(PNS)of nervous system.After OFA treatment(20 mg/time),the symptoms were obviously improved.This paper analyzes the clinical features and diagnosis and treatment approaches of this case,in order to improve clinicians'understanding of the disease and provide reference for clinical diagnosis and treatment of similar cases.