Objective: This ex post facto research was set to study the association of stress, religious attitude, and knowledge with maternal acceptance for sons with mental retardation (MR). Method: 107 mothers were selected using a multistage cluster method (stage1: exceptional schools of boys; and stage 2: class). Parenting stress index, religious attitude scale, and inventory of MR knowledge was administrated. Results: ANOVA and multiple regression analysis displayed that mothers with higher parenting stress were less acceptant. Also, acceptance was significantly different among three SES levels. More religious mothers were highly acceptant, and mothers with more knowledge about MR were also more acceptant. The findings showed that more religious mothers experienced less parenting stress. On the other hand, mothers with more knowledge about MR experienced less parenting stress. Conclusion: This study revealed that a significant relationship exists between parenting stress, religious attitude, knowledge about mental retardation and acceptance by mothers.