We investigated the relationship between burnout and communication skill training among Japanese hospital nurses to improve the mental health of human service workers. The subjects were forty-five registered nurses referred to a self-expression skill intervention program by their section superiors, with each superior choosing from two to five nurses. The hospital was located in the Kyushu area and staffed by about four hundred nurses. The subjects were divided into an intervention group (19 nurses) and a reference group (26 nurses). The intervention group received the communication skill training in July and August, 2001. The communication skill training was carried out in accordance with the assertiveness training (AsT) precepts of Anne Dickson. In June, 2001, we delivered a set of questionnaires including age, gender, working years, a burnout scale, and a communication skill check-list as a baseline survey. The baseline questionnaires were returned at the end of June, 2001. In January, 2002, we delivered the same questionnaire again to the two groups and collected them at the end of the month. Excluding the only male and insufficient answers, twenty-six nurses (58%) returned complete answers in the initial and subsequent surveys. We found that the personal accomplishment and the two communication skills such as "accepting valid criticisms" and "negotiation" of the intervention group had improved significantly five months after the training as compared with that of the reference. Our results implied that communication skill training might have a favorable effect on burnout among Japanese hospital nurses.