The principal factors of adolescent school phobia are often attributed to interpersonal anxiety.The present case was also in the state of maladjustment due to interpersonal anxiety.The author treated a case of adolescent school phobia by using asssertive training and systematic desensitization produres with marked success.Impressions were summarized as follows : 1) Behavior therapy was effective in this patient with adolescent school phobia.2) The sysmptom of this disorder would spontaneously be removed if (a) noxious stimuli and the anxiety reaction were precisely grasped, (b) abnormal reactions to those noxious stimuli were released and (c) a new adaptive behavior was leaned.