Background and Purpose: Children with intellectual disability may cause growing psychological problems for their parents, specifically the mothers as the principal caregivers. During the recent years, different research and clinical methods have been used to reduce these psychological problems. Present research was conducted to compare the effectiveness of emotion regulation training and mindfulness training on the reduction of rumination in the mothers of children with mild intellectual disability. Method: This study was a quasi-experimental research with multi-group pretest-posttest design. The population included all the mothers of children with mild intellectual disability who had referred to the special schools of Rasht in the academic year 2019-2020. Among them, a sample of 36 mothers was selected by purposive sampling and then randomly assigned into the experimental or control groups (12 mothers per group). To collect the data, Ruminative Response Scale (Nolen-Hoeksema & Morrow, 1991) was used. After nine 90-min sessions of emotion regulation training and mindfulness training conducted for the experimental groups, all the three groups were reassessed at the post-test stage. Data were analyzed by one-way ANCOVA and multivariate ANCOVA in SPSS-22. Results: Data analysis showed that emotion regulation training and mindfulness training significantly decreased the overall rumination and its components in the mothers of children with mild intellectual disability (P<0.01). Furthermore, based on the results of post hoc tests, it can be said that there was no significant difference between emotion regulation training and mindfulness training in reducing the overall rumination and its components (P>0.05). Conclusion:Based on these findings, it can be said that emotion regulation by improving the emotional repair, reducing the negative self-referential processing, and increasing the ability of doing purposive behaviors, and mindfulness training by increasing the present moment awareness and more efficient information processing are effective in reducing rumination in the mothers of children with mild intellectual disability.