A 72-year-old woman developed a subacute series of encephalitis, cerebellar ataxia, and combined symptoms of both myasthenia gravis and Lambert-Eaton myasthenic syndrome. Seven different neuronal antibodies were detected for Hu, glutamic acid decarboxylase, acetylcholine receptor, P/Q-type voltage-gated calcium-channels, Zic4, Titin and SOX1 in her serum with intrathecal synthesis of glutamic acid decarboxylase antibodies. Although she showed classical manifestations with onconeural antibodies, she was diagnosed with not paraneoplastic but autoimmune neurological syndrome because of no underlying tumor and good response to immunotherapies. The present case is very unique and rare for complex neurological disorders including myasthenia gravis and Lambert-Eaton myasthenic syndrome overlap syndrome with multiple neuronal antibodies.