The purpose of this study was to evaluate the effect of the behavior modification on improving hyperphosphatemia in the hemodialysis patients. A quasi-experimental with two-group pretest-posttest design was used. The subjects were selected from the hemodialysis center of a hospital in Taipei and their serum phosphorus value was above 6.0 mg/dl in August, 2004. Subjects were divided by random assignment into an experimental group and a control group. They fulfilled the questionnaires of relative phosphoric knowledge and behavior before research. The experimental group received behavior modification, whereas the control group received only regular hyperphosphatemia nursing care. They then were written again the questionnaires and taken blood sample for phosphorus value in September. The results indicate that both groups experienced the improvements of knowledge, behavior and serum phosphorus value. Only serum phosphorus value of the experimental group was in the normal range. Study results may provide to improve hemodialysis patients' serum phosphorus value.