Many women suffer from daily distressing symptoms related to lymphedema following breast cancer treatment. Lymphedema, an abnormal accumulation of lymph fluid in the ipsilateral body area or upper limb, remains an ongoing major health problem affecting more than 40% of 3.1 million breast cancer survivors in the United States. Patient-centered care related to lymphedema symptom management is often inadequately addressed in clinical research and practice. mHealth plays a significant role in improving self-care, patient-clinician communication, and access to health information. The-Optimal-Lymph-Flow health IT system (TOLF) is a patient-centered, web-and-mobile-based educational and behavioral mHealth interventions focusing on safe, innovative, and pragmatic electronic assessment and self-care strategies for lymphedema symptom management. The purpose of this paper is to describe the development and test of TOLF system. The development of TOLF was guided by the Model of Self-Care for Lymphedema Symptom Management and designed based on principles fostering accessibility, convenience, and efficiency of mHealth system to enhance training and motivating assessment of and self-care for lymphedema symptoms. Test of TOLF was accomplished by conducting a psychometric study to evaluate reliability, validity, and efficiency of the electronic version of Breast Cancer and Lymphedema Symptom Experience Index (BCLE-SEI), a usability testing and a pilot feasibility testing of mHealth self-care interventions. Findings from the psychometric study with 355 breast cancer survivors demonstrated high internal consistency of the electronic version of the instrument: a Cronbach's alpha coefficient of 0.959 for the total scale, 0.919 for symptom occurrence, and 0.946 for symptom distress. Discriminant validity of the instrument was supported by a significant difference in symptom occurrence (z=-6.938, P<0.000), symptom distress (z=-5.894, P<0.000), and total scale (z=-6.547, P<0.000) between breast cancer survivors with lymphedema and those without it. Findings of usability testing showed that breast cancer survivors were very satisfied with the mHealth self-care interventions: 90% rated the system having no usability problems; 10% noted minor cosmetic problems: spelling errors or text font size. The majority of participants 96.6% strongly agreed that the system was easy to use and effective in helping to learn about lymphedema, symptoms and self-care strategies. Feasibility testing demonstrated that a 12-week one group intervention using TOLF had significantly positive effects on less pain (P=0.031), less soreness (P=0.021), less aching (P=0.024), less tenderness (P=0.039), fewer numbers of lymphedema symptoms (P=0.003), and improved symptom distress (P=0.000) at 12 weeks after intervention. Themes from the qualitative data included empowerment, high quality information, loving avatar simulation videos, easy accessibility, and user-friendliness. TOLF system using the electronic version of the instrument is able to assess patients' lymphedema symptoms with high reliability and validity. TOLF system is also able to deliver self-care interventions to enhance self-care strategies for lymphedema symptom management.