Abstract: Disclosed are brain connectivity marker of sustained pain and a method of diagnosing sustained pain using the same. The marker is specific for pain, and does not respond to other noxious stimuli. It can be used for monitoring a pain level and a response to treatment of chronic pain patients, which are considered clinically significant. By comparing a responsive clinical pain group and a non-responsive clinical pain group, the disclosure may be used for differential diagnosis for the cause of pain. The disclosure may be used for pre-screening of a drug clinical trial to dramatically reduce time and costs consumed in trial, and contributes to the development of pain treatment methods such as brain stimulation based on a weight pattern of the marker. The disclosure maybe used to measure a pain level in groups which have difficulty in reporting pain (a vegetative state, aphasia patients, the elderly, infants, etc).