The present study was conducted to investigate the efficacy of acceptance and commitment therapy on the cognitive fusion and self-care behaviors of the students with type-1 diabetes. It was a quasi-experimental study with pretest, posttest, with control group design. The follow-up period was administered in two months too. The statistical population of the present study included first- and second-grade high school students with type-1 diabetes in the town of Lar in academic year 2021-22. Thirty six students with type 1 diabetes were selected through purposive sampling method and randomly accommodated into experimental and control groups. The experimental group received ten sessions of acceptance and commitment therapy during two-and-a-half months. The applied questionnaires included Cognitive Fusion Questionnaire (CFQ) (Gillanders, et.al, 2010) and Self-Care Questionnaire (SCQ) (Galiana, et.al, 2015). The collected data were analyzed through mixed ANOVA via SPSS23 software. The results showed that acceptance and commitment therapy has significant effect on the cognitive fusion and self-care behaviors of the students with type-1 diabetes (p<0.001). According to the findings of present study it can be concluded that acceptance and commitment therapy can be used as an efficient treatment to decrease cognitive fusion and improve self-care behaviors in the students with type-1 diabetes through applying techniques such as six main processes including psychological acceptance, context self, communication with the present time, values and committed action.