Aim: The present study aimed to determine the effectiveness of forgiveness skill training on marital conflict and aggression in parents of deaf children. Methods: The present research was a quasi-experimental study by pre-test, post-test design with control group. Thirty parents of deaf children were selected by convenient sampling method from exceptional schools in Tehran city. They were divided into experimental and control group (each consists of 15 individuals) randomly and equally. The experimental group participated in forgiveness skill training in 8 sessions (two sessions weekly; each lasts for 70 minutes), while control group did not. Marital conflict questionnaire and aggression questionnaire were used for assessment of all participants. Data were analyzed by multiple analysis of covariance through SPSS version 22. Results: Findings showed that experimental and control groups had significant difference, at least in one of the marital conflict and aggression variables (P<0.05). The results of multiple analysis of covariance showed forgiveness skill training had positive and significant effect on the marital conflict and aggression in parents of deaf children (P<0.05). Conclusion: Findings indicated that forgiveness skill training has led to the reducing marital conflict and aggression in parents of deaf children. Therefore, planning for such training programs alike with the forgiveness training has an important role on reducing marital conflict and aggression in parents of deaf children.