This research set out to examine the effectiveness of purposeful-based Multiple Family Group Therapy in development of purposeful thinking among adolescents. The statistical population of the study was comprised of all female 12^th graders studying in public high schools in Bojnord. The research sample consisted of 34 volunteers who were randomly assigned to three groups of experimental, sham-control and control groups and were administered the Youth Purpose Survey in three the stages of the research, i.e., pretest, posttest, and follow-up. Subjects in the experimental group were given the 10-session purposeful-based MFGT intervention and the subjects in the sham-control group participated in 10 group sessions without any intervention protocol. The data were analyzed via descriptive methods and chi-square in three stages of assessment. Results indicated that purposeful-based MFGT can effectively develop purposeful thinking among adolescents through taking advantage of the inner strength of families and directing the communication style of the adolescent-parent. Subjects in the sham-control group had experienced a slight reduction in their intra-family conflicts due to attending group sessions; however, this change was not significant enough in such a way that it could influence their thinking style. And finally, subjects in the control group did not experience any change in their family relationships and thinking styles.