There have been several reports about coexistence of myasthenia and other autoimmune disease. Psoriasis is a papulosquamous disease defined by erythematous plaques with a silvery scale and a T-cell-mediated autoimmune disease. We report a case of a 49-year-old an with generalized myasthenia gravis (MG) superimposed by psoriasis. MG was diagnosed by clinical symptoms, increased acetylcholine receptor antibody titer and repetitive nerve stimulation test. Psoriasis was diagnosed by clinical manifestations and specific skin biopsy findings. MG and psoriasis are both autoimmune diseases. The coexistence of MG and psoriasis suggest a close connection of pathogenesis.