Young women are gaining weight rapidly. Evidence for effective weight loss interventions targeting young women is lacking. This randomized controlled trial assessed the efficacy and acceptability of a six-month targeted and tailored eHealth weight loss program for young women (Be Positive Be Healthe
(BPBH)). Women aged 18–35 years were randomized to BPBH (n
= 29) or control (n
= 28). BPBH supported participants to modify diet and physical activity behaviours using evidenced-based strategies (e.g., self-monitoring) tailored for young women and delivered using e-health (website, social media, smartphone application, email, text messages). The primary outcome was a change in weight (kg) at six months. Acceptability was assessed via a process evaluation survey and usage of intervention components. No significant between-group differences were observed for weight, with significant mean differences favouring the intervention group observed for body fat (kg) (−3.10 (−5.69, 0.52), p
= 0.019) and intakes of alcohol (g) (−0.69 (−1.33, 0.04), p
= 0.037), vegetables (% energy/day) (4.71 (−2.20, 7.22), p
< 0.001) and energy-dense, nutrient-poor foods (% energy/day) (−9.23 (−16.94, 1.52), p
= 0.018). Retention, intervention usage and satisfaction were moderate. BPBH facilitated positive improvements in body fat and dietary intake, but not weight. Intervention acceptability findings support the use of some intervention components (e.g., Facebook, Smartphone app) with young women.