INTRODUCTION: Sleep problems are a characteristic feature of children with autism spectrum disorder (ASD) with 40% to 80% of children experiencing sleep difficulties. Sleep problems have been found to have a pervasive impact on a child's socio-emotional functioning, as well as on parents' psychological functioning. The Sleeping Sound ASD project aims to evaluate the efficacy of a brief behavioural sleep intervention in reducing ASD children's sleep problems in a fully powered randomised controlled trial (RCT). Intervention impact on child and family functioning is also assessed. METHODS AND ANALYSIS: The RCT aims to recruit 234 children with a diagnosis of ASD, aged 5-13 years, who experience moderate to severe sleep problems. Participants are recruited from paediatrician clinics in Victoria, Australia, and via social media. Families interested in the study are screened for eligibility via phone, and then asked to complete a baseline survey online, assessing child sleep problems, and child and family functioning. Participants are then randomised to the intervention group or treatment as usual comparator group. Families in the intervention group attend two face-to-face sessions and a follow-up phone call with a trained clinician, where families are provided with individually tailored behavioural sleep strategies to help manage the child's sleep problems. Teacher reports of sleep, behavioural and social functioning are collected, and cognitive ability assessed to provide measures blind to treatment group. The primary outcome is children's sleep problems as measured by the Children's Sleep Habits Questionnaire at 3 months post-randomisation. Secondary outcomes include parent and child quality of life; child social, emotional, behavioural and cognitive functioning; and parenting stress and parent mental health. Cost-effectiveness of the intervention is also evaluated. ETHICS AND DISSEMINATION: Findings from this study will be published in peer-reviewed journals and disseminated at national and international conferences, local networks and online.