OBJECTIVES: To determine the feasibility and preliminary effectiveness of a group dynamics-based exercise intervention versus a personal training intervention for increasing physical activity (PA), physical fitness, and quality of life (QOL) in posttreatment breast cancer survivors. SAMPLE & SETTING: 26 women with stage I or II breast cancer who attended intervention activities at a local academic institution. METHODS & VARIABLES: Participants were randomly assigned to receive an eight-week intervention in either a group dynamics-based exercise or a personal training setting. Both intervention arms received supervised exercise twice per week, as well as PA education and discussion sessions. RESULTS: Significant increases were noted in both intervention arms for vigorous PA, chest press, and leg press. Increases in overall QOL and total PA were significant only in the group dynamics-based exercise intervention arm. IMPLICATIONS FOR NURSING: The group dynamics- based exercise intervention produced similar improvements in PA and physical fitness compared to the personal training intervention, and it may have facilitated greater improvements in overall QOL.