【Background】Child maltreatment recidivism substantially increases the likelihood of adverse life outcomes, but there is little evidence that family preservation services are effective at reducing recidivism. Mothers in child welfare have very high rates of trauma exposure; maternal post-traumatic stress disorder (PTSD) is an intervention target that has the potential to reduce abuse and neglect. The Safe Mothers, Safe Children (SMSC) intervention program involves the delivery of an innovative combination of interventions, including Skills Training in Affective and Interpersonal Regulation (STAIR) and Parent-Child Interaction Therapy (PCIT). The combined intervention, Parenting-STAIR (P-STAIR), targets maternal PTSD and comorbid depression symptoms to reduce the adverse effects of PTSD on parenting, improve positive parenting skills, and prevent maltreatment recidivism.【Methods】This study is a two-arm randomized controlled trial: P-STAIR (23 sessions) versus supportive counseling (23 sessions). Participants are mothers receiving child welfare family preservation services (FPS), with a child in the age range of 1-8 years old and meeting diagnostic criteria for PTSD (with/without depression). Clinical assessment occurs at pre-treatment (baseline), two in-treatment assessments (mid-assessment #1 after module 9 and mid-assessment #2 after module 15), post-treatment, and at a 6-month follow-up. Recidivism will be measured using the New York State Child Welfare Registry (NYSCWR). We will enroll a total of 220 participants over 4 years: half (N = 110) randomly assigned to the P-STAIR condition and half (N = 110) to the supportive counseling condition.【Discussion】This is the first RCT to investigate the efficacy of P-STAIR. The findings for the trial have the potential to contribute to the expansion of evidence-based practices for maternal PTSD, maltreatment, and child welfare.