The authors developed a structured group intervention for Japanese breast cancer patients. This program is a series of five 90-minute sessions including psycho-education, problem-solving, psychological support, relaxation training, and guided imagery. The aim of this study was to investigate discriminating factors between the improving and non-improving group. From November 1996 through November 1998, 110 patients participated in this study. Out of 110 patients, 9 failed to complete the five sessions. Nine did not return the questionnaire 6 months later, due to death of 3 individuals and re-location of 6. The remaining 92 patients were analyzed. The subjects were administered the Profile of Mood States (POMS) at entry and 6 months after the completion. According to the overall change in Total Mood Disturbances scores of the POMS, 69 subjects were categorized into the improving group and 23 into the non-improving group. This study defined several factors which discriminated between the improving and the non-improving group. These factors can be summarized as: (1) 'good relationship with doctors', (2) 'family support/understanding', (3) 'more intervention benefit', and (4) 'no comorbid adjustment disorders' at entry. Further modification is suggested such as an educational approach for family members to increase their understanding/support and also additional support for patients with adjustment disorders is suggested.