This systematic review protocol aims to examine the evidence of effectiveness and cost-effectiveness of interventions for children and adolescents with, or at risk of developing mental disorders in low- and middle-income countries (LAMICs).We will search Medline Ovid, EMBASE Ovid, PsycINFO Ovid, CINAHL, LILACS, BDENF and IBECS. We will include randomised and non-randomised controlled trials, economic modelling studies and economic evaluations. Participants are 6 to 18 year-old children and adolescents who live in a LAMIC and who present with, or are at high risk of developing, one or more of the conditions: depression, anxiety, behavioural disorders, eating disorders, psychosis, substance abuse, autism and intellectual disabilities as defined by the DSM-V. Interventions which address suicide, self-harm will also be included, if identified during the extraction process. We will include in person or e-health interventions which have some evidence of effectiveness (in relation to clinical and/or functional outcomes) and which have been delivered to young people in LAMICs. We will consider a wide range of delivery channels (e.g., in person, web-based or virtual, phone), different practitioners (healthcare practitioners, teachers, lay health care providers) and sectors (i.e., primary, secondary and tertiary health care, education, guardianship councils). In the pilot of screening procedures, 5% of all references will be screened by two reviewers. Divergences will be resolved by one expert in mental health research. Reviewers will be retrained afterwards to ensure reliability. The remaining 95% will be screened by one reviewer. Covidence web-based tool will be used to perform screening of references and full text paper, and data extraction.The protocol of this systematic review will be disseminated in a peer-reviewed journal and presented at relevant conferences. The results will be presented descriptively and, if possible, meta-analysis will be conducted. Ethical approval is not needed for anonymised secondary data.the systematic review could help health specialists and other professionals to identify evidence-based strategies to deal with child and adolescents with mental health conditions.