Parents of children with medical complexity (CMC) are suffering from high level of stress. These CMC get multisystem diseases, including severe neurologic conditions or cancer, resulting in potential premature death. They experience one or more physical and psychological symptoms at one time, which seriously affect their quality of life and increase their health services utilization. Parents may lack confidence in their abilities when managing their child's symptoms. Literature suggested that increasing parental self-efficacy in managing their child's symptoms could improve child's health status. Home-based nursing services for the CMC and parents are available in Hong Kong. However, the service faces challenges because of serious nursing workforce shortage and the recent coronavirus pandemic. Nurse parental support in symptom management using a proactive mobile health App is an alternative method considered more feasible to continue home-based support for the CMC and parents. This proposed RCT will test the effects of a nurse-led mobile App for enhancing parental self-efficacy in symptom management for CMC. A repeated-measures, two-group design will be used to evaluate the effects between intervention and wait-listed control groups by comparing the study group receiving nurse support using a mobile App, and the wait-listed control group receiving usual community care for 96 randomly selected parents over a three-month follow-up. Primary outcome is parental self-efficacy. Secondary outcomes include children's symptom burden and health services utilization. These factors will be measured before intervention, immediately after intervention and three-month after intervention. The effectiveness of the intervention will be evaluated by comparing the primary outcome at three-month after intervention across the two study groups using ANCOVA with control for the pre-test value of parental self-efficacy. Generalized estimating equation will be used to address secondary objectives regarding the effectiveness of the mobile App as compared to the control on secondary outcomes from T1 to T3 with appropriate link function. It is hypothesized that nurse support using the mobile App is more effective than usual community care in enhancing parental self-efficacy in symptom management for their CMC at three-month after intervention.