[Purpose] Lambert-Eaton myasthenic syndrome (LEMS) is an autoimmune disease characterized by decreased transmitter secretion from neuromuscular junctions and nerve terminals. Such cases require physical therapy for independently performing daily activities; however, care must be taken to avoid overwork weakness. This study aimed to investigate the effects of aerobic exercise-based physical therapy in patients with LEMS. [Participants and Methods] We report a case of LEMS with decreased muscle endurance due to inactivity. The participant was subjected to physical therapy with an exercise modality-improved muscle endurance with low-intensity repetitions, while monitoring subjective exercise intensity over time. [Results] The participant achieved independence activities of daily living without developing overwork weakness. [Conclusion] Appropriate physical therapy is an important aspect in treating LEMS.