Body dissatisfaction has been related to Body Image Disorders (BIDs) such as Eating Disorders (EDs) and Body Dysmorphic Disorder (BDD). This study investigates the efficacy of a mHealth app in reducing body dissatisfaction, BDD/ED symptoms and related features. Ninety-five women who were identified as high-risk of developing BIDs (using the Structured Clinical Interview for DSM-5) were randomized into: immediate-use App (iApp group; n = 47) and delayed-use App (dApp group; n = 48). The iApp group started using the app at baseline for 16 days (T1). The dApp group started using the app at T1 for 16 days. Participants completed questionnaires at baseline (T0), 16 days from baseline (T1), and 32 days from baseline (T2). Repeated measure Multivariate Analysis of Variance (MANOVA) showed Group (iApp vs. dApp) × Time (T0 vs. T1) interactions indicating decrease in BDD symptoms and body dissatisfaction related to EDs in the iApp group at T1. The Reliable Change Index indicated changes on extreme body dissatisfaction/BDD symptoms for 34.74% of participants. Although preliminary, these findings highlight that a mHeatlh app might reduce BDD symptoms and body dissatisfaction related to EDs in women at high-risk for BIDs. Effects on ED symptoms and associated features seem more limited.