This study aimed to investigate the effectiveness of parent-child interaction therapy on loneliness, aggression, and self-efficacy in children of divorce. The research method was quasi-experimental with a pretest-posttest control group design. The statistical population of the study included all children of divorce with files at the welfare centers of Babol County in the year (2026–2027), whose number was reported as 743 based on the obtained statistics. From this statistical population, using purposive sampling method and based on inclusion and exclusion criteria, 30 eligible children were selected. After administering the pretest, participants were randomly assigned to two groups: an experimental group and a control group. The experimental group received parent-child interaction therapy sessions, while the control group remained on a waiting list. The research instruments included the Morris Self-Efficacy Questionnaire (2002), the Asher et al. Loneliness Questionnaire (1984), and the Nelson et al. Aggression Questionnaire (2000). The face validity of the instruments was confirmed by experts, and their reliability was reported at a desirable level using Cronbach's alpha coefficient. Data analysis was conducted in two sections—descriptive statistics and inferential statistics—using SPSS software version 26. The results of the study indicated that parent-child interaction therapy had a significant effect on reducing loneliness, reducing aggression, and increasing self-efficacy in children of divorce (p < 0.05). The findings of this research suggest that parent-child interaction therapy, by strengthening positive parent-child interactions, increasing emotional support, improving communication quality, correcting dysfunctional interaction patterns, and creating positive communicative experiences, can be used as an effective approach in improving the emotional and behavioral adjustment of children of divorce.