Abstarct: The present research is aimed to investigate the effect of eight weeks of aerobic training in water on plasma levels of beta endorphin and level of quality of life among veterans with spinal cord injury. The present research is of semi-experimental, the research model is comparative, and it is of applied type. For this research, among 70 volunteered veterans with spinal cord injury, 30 individuals, who had inclusion criteria, were selected randomly and included in the study. These individuals were divided into three groups of active in water, active on ground, and control. After completing the Quality of Life Questionnaire, and bloodletting for assessing beta endorphin levels, experiment groups, which are active in water and active on ground groups, performed their aerobic activity with the intensity of 80 heart-rate max in three session per week training for eight weeks. The results suggested that total criterion of quality of life in veterans with spinal cord injury improved significantly for both active in water and active on ground groups (P < .01). it was shown also that in-water trainings had significantly (.99 confidence level) more effect on improving quality of life in comparison to on-ground training. Investigating plasma level variations for beta endorphin also showed that eight weeks of training has led to significant increase of this hormone in both active in water and active on ground groups (P< .01), and it was also shown that aerobic activity in water has led to significantly more effect on increasing plasma level of beta endorphin (.95 confidence level). Therefore, it seems that using aerobic training can be one of the available sources for veterans with spinal cord injury, by which they can have better quality of life and higher beta endorphin level.