Families with adolescents need to deal with increased anxiety in parent-adolescent relationships and make adjustments to adolescents' psychological development (Carter & McGoldrick, 2005). In Taiwan, mothers are the main carers of children in families (Taiwan Executive Yuan, 2011), and play a major role in the emotional and personality growth of adolescents (Bartle-Haring, Brucker, & Hock, 2002).  However, research has pointed out that mothers tend to have huge emotional problems and anxieties with parenting, which might result from inadequate mother-adolescent boundaries, as well as the anxieties of the mothers themselves, family members, and society expectations (Gilbert, 1999). In order to help mothers with adolescents to deal with their parenting anxiety and have better relationships with their adolescent children, some parenting educators and researchers have advocated the application of family system theories in parenting groups (Ham, 2011). This study aimed to examine and explore the effects of a parenting group based on Bowen theory for mothers with young adolescents in Taiwan. An embedded quasi-experimental design of mixed method research was used for the study. The primary purpose of this study was to examine the effects of the parenting group on reducing mothers' anxiety toward the parent/adolescent relationship, enhancing differentiation within the mother/child subsystem, as well as increasing participants' emotional maturity. The secondary purpose of this study was to explore participants' personal experiences and understandings of the parenting group in the changes among oneself, the mother/adolescent relationship, as well as the family systems. The group model consisted of eight two-hour sessions for a total of sixteen hours for eight successive weeks. Participants were eleven mothers with at least one young adolescent child in Taipei, and they participated in either the experimental group or the comparison group. Both quantitative and qualitative methods were used. Quantitative data were pre-test and post-test scores on Chinese versions of the Differentiation in the Family System Scale (DIFS-Chinese version) and Differentiation of Self Inventory-Revised (C-DSI) in each of the two groups. Participants' anxiety toward the mother/adolescent relationship was assessed in the experimental group by a group observer in each group session, and their follow-up scores on the DIFS-Chinese version and C-DSI were collected four weeks after the group ended. Qualitative data were collected by a focusgroup interview for participants one week after each of the two groups ended. Mean scores on the group observation assessment showed that participants' anxiety toward the mother/adolescent relationship decreased about 50% in the first and final group sessions. Results of the ANCOVA analyses and dependent t-tests indicated that there were immediate and follow-up effects on increasing differentiation within the mother/child subsystem for the experimental group. However, no immediate or follow-up effects on improving participants' emotional maturity were found. Further, qualitative data were coded and analyzed using thematic analysis, and findings revealed that the parenting group provided participants with assistance in their intrapersonal changes as well as supporting positive changes in their mother/adolescent relationships and in their family systems. In terms of their intrapersonal changes, participants gained insights and made adjustments on their mother roles and expectations to decrease their anxiety and emotional reactivity toward their adolescent children. As for the positive changes in their mother/adolescent relationships, participants made some adjustments in the mother-adolescent boundary. They started to understand and respect adolescent children's autonomy needs and decisions, and tried to make a positive connection with them. Further, their mother-adolescent conflicts dampened. Even though the number of conflicts did not decrease, participants acquired some strategies to make themselves calm down to be able to deal with the conflicts more effectively. In addition, in terms of the changes within their family systems, some participants reported that their husbands' relationships with adolescent children had improved, and others mentioned that interactions with other family members such as their own mothers and another child had also improved. Findings of this study suggested that a parenting group based on Bowen Family Systems Theory can help mothers with young adolescents to decrease their anxiety and improve their differentiation with their adolescent children. Implications of the findings for the parenting group based on Bowen theory as well as suggestions for the future study are discussed.