Introduction: the presence of mentally retarded child in the family causes various psychological problems in the parents. Among the variables affected by the presence of disabled child in the family are hope, life quality and psychological well-being. Therefore the present study was conducted to investigate the effect of hope therapy on the improvement of life quality, hope and psychological well-being in mothers of mentally retarded children.
 Method : it was semi-experimental, with pretest, posttest, and control group format because of available sampling. The statistical population included all the mothers of mentally retarded children in Isfahan. In order to do the study 60 mothers of mentally retarded children were selected through available sampling. Therefore the criterion to enter the study was having a mentally retarded child and readiness to take part in the research and the criterion to exit was having a child with a disorder or other inabilities. The experimental groups participated in 8 ninety-minute sessions of hope therapy however, the control group didn't receive any intervention while administering the test. The applied instruments were the questionnaires of hope, psychological well-being and life satisfaction.
Findings: the results showed that teaching hope therapy has led to significant difference in the mean of experimental group scores in all three variables of life quality, hope and psychological well-being (p<0.01).
Conclusion: hope-based therapy could improve the hope, psychological well-being and life quality in the parents of mentally retarded children due to focusing on the major problem and attending solely on the concept of hope. Therefore, through utilizing this therapeutic approach is recommended to solve the families' psychological dilemmas.