Background: Hardiness as a fundamental element of control plays a constructive role in coping with stress and moderates the effects of stress. This study aimed to compare the effectiveness of group-based Acceptance and Commitment Therapy (ACT) and group-based Cognitive-behavioral Therapy (CBT)in the psychological hardiness of single mothers. Methods: The research was conducted using a quasi-experimental pretest-posttest design with control group. Also, the statistical population included all female-headed families in the region 16 of Tehran. From women with low scores in the Ahvaz psychological hardiness questionnaire, 45 women were randomly selected and assigned into three groups: two experimental and one control group. The acceptance and commitment and cognitive-behavioral therapies were implemented in the first and second experimental groups, respectively; the control group did not receive any intervention. The experimental groups received nine training sessions. Then, the study hypotheses were tested using the 1-way analysis of covariance. Results: Both interventions effectively increased the psychological hardiness in the single mothers, but no significant difference was found between the two intervention groups (P=0.38). Conclusion: According to the results, it is possible to increase the psychological hardiness of the single mothers by group-based acceptance and commitment therapy and group-based cognitive-behavioral therapy.