Background: Previously we developed a structured case management for multimorbid chronically ill patients in primary care (called ‘PraCMan’), delivered by Health Care Assistants in General Practice (VERAHs). The ‘TelePraCMan’ project aims to develop a supplementary web-based application to ‘PraCMan’, including a digital symptom diary in which patients can enter individual data via smartphone/tablet. This application is targeted at patients suffering from diabetes mellitus type 2, COPD, hypertension and/or chronic heart failure. Objective: The objective of this study is to evaluate this mHealth-intervention for patients with chronic diseases, focused on patients’ quality of life and self-management capabilities.Methods: A two-arm patient-randomized pilot trial is planned, involving 200 multimorbid patients in 20 GP-practices that use ‘PraCMan’ regularly. Participants are randomly assigned (1:1) to receive either standard ‘PracMan’ treatment or standard ‘PracMan’ treatment complemented with the mHealth-intervention (TelePraCMan). As primary outcome, the health-related quality of life is measured by the German version of the Short Form Health Questionnaire (SF-12). Secondary outcomes include self-management capabilities, technical affinity, and user experience of patient and practice staff. Outcomes are measured at baseline (T0) and at follow-up after 6 months (T1). For assessment of the implementation process, GPs, VERAHs and patients will be invited to participate in interviews afterwards.The outcomes will be compared between study arms, using multilevel regression analysis. Qualitative interviews will be transcribed and analyzed using qualitative content analysis. Discussion: ‘TelePraCMan’ is one of the first mHealth-Interventions addressing multimorbid patients in primary care in the research literature.Trial registration: DRKS, DRKS00017320, Registered 18 June 2019, http://www.drks.de/DRKS00017320