The pathologic laughing is involuntary and associated with brain damage seen in a variety of disorders, which occurs as a result of lesions in various locations and is often seen associated with prefrontal or brainstem lesions. Neuromyelitis optica spectrum disorder (NMOSD) is an autoimmune inflammatory disease of the central nervous system characterized by severe attacks of optic neuritis and myelitis, and also develops brain lesions involving the bilateral diencephalic regions adjacent to the third ventricles, the brainstem and cerebellum surrounding the fourth ventricles, and the periventricular white matter adjacent to the lateral ventricles. Emotional incontinence refers to episodic laughing or crying, and occurs as a result of brain damage in various locations and is often seen associated with prefrontal or brainstem lesions. Emotional incontinence has been well described in multiple sclerosis, however the emotional incontinence in NMO has not been systemically documented. My report a characteristic patient with NMO showing the pathologic laughing as an initial manifestation, and the plasmapheresis therapy showed remarkable improvement in severity and occurrence of the pathologic laughing.