A luminance calibration system and method of mobile device display for medical images is provided, and allows a mobile device display to display the medical images complying with grayscale standard display function (GSDF) defined by Digital Imaging and Communications in Medicine (DICOM) under any environmental light sources; for example, the medical images displayed by the mobile device display can meet a Just-Noticeable Difference (JND) defined by DICOM to facilitate medical diagnosis for medical staffs. In addition, the luminance calibration system and method of mobile device display for medical images only adjusts the medical images inside the operating window of the mobile device display, while any image outside the operating window of the mobile device display is reserved; as a result, the luminance calibration system and method of mobile device display for medical images makes the mobile device display to be a medical image screen as well as a regular screen.