Postpartum weight retention contributes to long-term weight gain and obesity for many women. Lifestyle interventions with numerous visits are logistically challenging for many postpartum women. Delivering a lifestyle intervention via social media may overcome logistic challenges to participation in in-person weight loss programs.The objective of this study is to conduct a randomized feasibility pilot trial of a 6-month postpartum weight loss intervention delivered via Facebook or in-person groups with 72 postpartum women with overweight or obesity.Women with overweight or obesity who are 8 weeks to 12 months postpartum (N=72) will be recruited from the Hartford, Connecticut community. Eligible participants must also own an iPhone or Android smartphone and be an active Facebook user. Participants will receive a 6-month postpartum weight loss intervention based on the Diabetes Prevention Program lifestyle intervention and adapted for postpartum women. Participants will be randomized to receive the intervention via a private Facebook group or in-person group meetings. Assessments will occur at baseline, weekly during the intervention, at 6 months (at the end of the intervention), and at 12 months. Primary feasibility outcomes are recruitment, sustained participation, contamination, retention, and feasibility of assessment procedures including measurement of costs to deliver and receive the intervention. We will describe 6- and 12-month weight loss as an exploratory outcome.Recruitment began in September 2018. The first wave of the intervention began in February 2019, and the second wave of the intervention is expected to begin in fall 2019. We anticipate completing follow-up assessments in fall 2020, and results will be analyzed at that time.Results will inform the design of a large randomized controlled trial to assess whether delivering a postpartum weight loss intervention via Facebook is noninferior for weight loss and more cost-effective than delivering the intervention via traditional in-person groups.DERR1-10.2196/15530.