Objective: The aim of this study is to evaluate a training in non-violent resistance (NVR) for foster parents who take care of a foster child (ages 6-18) with externalizing problem behavior. Methods: A randomized controlled trial was used to compare an intervention group (NVR, n = 31) with a treatment as usual control group (TAU, n = 31). The NVR-intervention consists of ten weekly home sessions. Measures regarding behavioral problems in foster children, parenting stress and parenting practices in foster mothers, and the size of the supportive network were assessed before, after treatment, and at three months follow-up. Results: NVR showed to be an acceptable approach that lead to an increase in experienced support and some promising changes in parenting stress and parenting practices. Conclusion: Implementation of this intervention might increase the effectiveness of foster care. More longitudinal research using a Multitrait-multimethod-approach is however needed.