Description: Introduction In previous studies, it has been found that on average, children consistently gained weight during the summer months at an increased rate compared with the 9-month school year. This contributed to an increased prevalence of overweight and obesity in children. Several obesity-related interventions have occurred during or targeting the summer months. We propose to conduct a systematic review and meta-analysis of the impact of obesity prevention and treatment interventions for school-age children conducted during the summer or targeting the summer months when children are not in school on their body mass index (BMI), or weight-related behaviours. Methods and analyses A literature search will be conducted by the first author (JPM) using MEDLINE/PubMed, Cochrane Library, Scopus, CINAHL, PsycINFO, EMBASE and Proquest Dissertations and Theses databases from the date of inception to present. Studies must examine interventions that address the modification or promotion of weight-related behaviours (eg, dietary patterns, eating behaviours, physical activity (PA), sedentary behaviour or sleep) and target school-age children (ages 5–18). The primary outcomes will be changes from baseline to postintervention and/or the last available follow-up measurement in weight, BMI, BMI percentile, standardised BMI or per cent body fat. Secondary outcomes will include changes in dietary intake, PA, sedentary behaviour or sleep. Risk of bias will be assessed using the Cochrane risk of bias tool for randomised and non-randomised studies, as appropriate. Ethics and dissemination Because this is a protocol for a systematic review, ethics approval will not be required. The findings will be disseminated via presentations at scientific conferences and published in a peer-reviewed journal. All amendments to the protocol will be documented and dated and reported in the PROSPERO trial registry. PROSPERO registration number CRD42016041750