Nurses face a great amount of stress that can threaten their health and reduce their motivation. Nurses’ most important stressful factors include working overload , being in close touch with patients’ death ,shift working, lack of psychological support, conflicts with the physicians, confusion in autonomy and progressive increase of bureaucratic process. This phenomenon can have destructive physiologic and psychological effects on nurses and negatively influence their health. On the other hand, stress , anxiety and depression reduce quality of patients’ care through increase of work events , delay and absenteeism and reduction of work efficiency and organizational commitment . Nurses’ present working conditions lead to an increase in emotional pressures and depression. There are various studies on the effect of happiness education on increase of happiness and reduction of stress, anxiety and depression in different social classes ,but the researcher found no studies, conducted among nurses taking care of cancer patients. Conducting such a study seems to be necessary ,with regard to nurses’ stressful working conditions, to take steps toward achieving different and non-medicational treatments to treat their stress , anxiety and depression and increase their happiness , and consequently, promote nurses’ and patients’ health. This study is a clinical trial to determine effect of happiness educational program on the level of nurses’ happiness , stress , anxiety , and depression in nurses (employed or working on a contract ) working in Seyed-Al-Shohada (peace on him) hospital for more than one year field two-group three- stage with sample size 52 subjects in study and control groups