ABSTRACT: Background:In the UK and beyond, public funding is used to commission interventions delivered in public health early years settings aimed at improving health and well-being and reducing inequalities in order to promote school readiness. This is a key setting for obesity prevention programmes, which are often commissioned despite the limited evidence base. The HENRY (Health, Exercise, Nutrition for the Really Young) programme is an 8-week programme delivered to parents of preschool children, designed to support families to optimise healthy weight behaviours. Early evidence suggests that it may be effective, but a robust evaluation using a randomised controlled design has not been conducted. This study begins this process by evaluating the feasibility of conducting a multi-centre definitive trial to evaluate the effectiveness and cost-effectiveness of HENRY to prevent obesity in the early years. Methods:This is a multi-centre, open labelled, two group, prospective, cluster randomised, controlled, feasibility study aiming to recruit 120 parents from 12 children's centres, based in two local authority areas. Within each of the two local authorities, three centres will be randomised to HENRY and three will be randomised to a control arm of standard care (usual provision of services within children's centres). We will explore HENRY commissioning, provision and delivery and assess the feasibility of local authority, centre and parent recruitment, the processes and time required to train and certify staff to deliver the intervention, the potential sources (and associated risk) of contamination and the feasibility of the trial procedures. Research includes a process evaluation, feasibility of cost-effectiveness evaluation, with progression to the definitive trial judged against pre-defined criteria. Discussion:This feasibility study will support the decision to proceed to, and the design of, a future definitive trial, providing an evidence base of an approach to prevent childhood obesity, which has been deemed attractive to all stakeholders, including parents. Given the widespread adoption of the intervention, this has the potential to impact on public health in the UK and beyond. Trial registration:ClinicalTrials.gov Identifier NCT03333733 registered 6th November 2017Protocol date: 25th October 2017Protocol version: 4.0.