To investigate the effect of a nurse support using a proactive mobile app to enhance parental self-efficacy in symptom management for children with medical complexity. A single-blinded, randomized controlled trial with a two-armed repeated measures design. Eligible parents and the children will be recruited from the special schools and non-government offices. They will be randomly assigned either to the intervention or control groups. Subjects in the study group will receive nurse parental support using a symptom management mobile app for 3 months. The control group will receive the usual care that is available in the community. Data will be collected pre-intervention (T1), immediately after the intervention (T2), and three-month after intervention (T3). The primary outcome is parental self-efficacy. The secondary outcomes include child's symptom burden and their health service utilization. Primary outcome will be compared across two groups in T2 and T3 using with control for the pre-test value of parental self-efficacy. Generalized estimating equation (GEE) will be used to address secondary objectives from T1 to T3 with appropriate link function. As a result of the successful implementation of this nurse-led symptom management, parental self-efficacy will be enhanced. Both the symptoms reported by the children and their health service utilization will be reduced. Findings of this study will help in service delivery improvements because it maximizes the availability and accessibility of paediatric health service to parents and the children in local communities. The evidence produced in this study will enlarge the knowledge base that supports evidence-based paediatric home nursing service with the use of health technology in symptom management. This evidence will also contribute to the development of other symptom management programs for other paediatric patient groups. NCT05765643 (ClinicalTrials.gov identifier). Parents of children with medical complexity contributed in mobile application development by giving comments on the usability of mobile application. Improve health service delivery: Home nursing service may not be sustainable in a long run in Hong Kong, as the health care system has been facing a serious nursing workforce shortage in recent years. Besides, these services are affected or even suspended during the community outbreak of infectious disease, like recent coronavirus disease pandemic. Nurse parental support in symptom management for the CMC using a proactive mobile health application will help in service delivery improvements because it maximizes the availability and accessibility of paediatric health service to parents and their CMC in local communities. Improve physical and psychological health of parents and their CMC: The success of program implementation will help to increase parental self-efficacy in symptom management for their CMC, as a result of decrease of children's symptom burden. Improve knowledge base: The evidence produced in this study will (1) enlarge the knowledge base that supports evidence-based paediatric community nursing service related to symptom management for the CMC. This evidence will contribute to the development of other symptom management programs for other paediatric patient groups.