Macrophage activation syndrome (MAS) involves an excessive amount of acute inflammatory responses to inflammatory cytokines, particularly interleukin-6 (IL-6). IL-6 is also strongly associated with the pathophysiology of certain neuroimmunological diseases. However, there have so far been few reports of MAS being accompanied by neuroimmunological diseases. We herein report two cases of MAS comorbid with myasthenia gravis or neuromyelitis optica spectrum disorders, IL-6 related neuroimmunological diseases. Standard immunosuppressive therapies could not stabilize the symptoms in our cases until antibodies against the IL-6 receptor were administered. This finding suggests that it is important to consider the underlying pathophysiology of MAS in relation to these neuroimmunological diseases when treating affected patients.