We report the case of an adolescent male who presented with mutism, immobility, catalepsy, and mannerisms. The patient was admitted to our hospital with suspected catatonic schizophrenia ; however, he was subsequently diagnosed with catatonia due to Asperger’s disorder. The patient was a 16-year-old male. More than six months before presentation,his grandfather displayed bizarre and violent behavior. Subsequently,he began to experience catatonia, which eventually led to hospitalization. Treatment with diazepam improved his condition and, as no causal disorders other than Asperger’s disorder were identified,he was diagnosed with catatonia. The patient had experienced persistent abuse by his mother during childhood ; therefore, it is important to consider reactive attachment disorder（DSM-IV-TR）as a differential diagnosis. Among child and adolescent psychiatrists, catatonia is considered to occur at a high frequency among patients with autistic spectrum disorders. In contrast, general psychiatrists tend to consider catatonia as related to schizophrenia,which may be the reason why the diagnosis of our patient was difficult. We assume that the pathogenesis of catatonia in this case was death mimicry due to the subjective perception of a life-threatening situation. For the treatment of catatonia with autistic spectrum disorders,the efficacy of benzodiazepines and electroconvulsive therapy has been established. When a patient with an autistic spectrum disorder presents with motor functional disturbances,it is important to consider these disturbances as catatonia. Furthermore, it is also important to begin the treatment mentioned above even in the presence of definite psychogenic or situational factors.