The aim of study is to develop and validate a Positive Psychotherapy based on Belief to Good in decreasing Depression. According this, the Single Subject Multiple Baseline Study will be conducted. The first, three patients with Signs and Symptoms of Depression that have Inclusion and Eexclusion criteria will choose from a Center of Counseling and Psychological Services in Tehran by Purposeful Sampling. An Inclusion criterion is: score 14-35 in Beck Depression Inventory-II. An Exclusion criterion is: Having symptoms of psychotic disorders. Each 3 participants are entered the Base line phase (from 3 to 7 week) at the same time. Then, Participants are randomly assigned in to treatment. Treatment is conducted by the Investigator in 8 sessions. Basic Acceptance, Freedom from judgment, Belief to Good in difficulty, Life Values, Identification Virtues and Strengths, Savoring, Gratitude, Active and Constructive Responding will run in sessions. Within Base line stage (3-7 weeks) Therapy phase (8 week) and Follow up steps (1 and 3 month after treatment), patients fill out Beck Depression Inventory (BDI-II), Hamilton Rating Scale for Depression-17, Orientations of Happiness, Positive And Negative Affect Scale (PANAS), Meaning in Life(MLQ), Riff’s Psychological Well-being Inventory, The Oxford Happiness Questionnaire and Satisfaction With Life Scale (SWLS). All of the assessment, in Baseline, Treatment process and Follow up is done by an MA in Psychology.