Chronic pain is thought to be a brain disease, but the mechanisms are not well-known. In recent years, brain imaging has become an indispensable tool for pain research. For example, nuclear molecular imaging is a safe and noninvasive technology that allows researchers to probe potential brain regions of interest with suitable biomarkers. These studies help us to understand the central mechanisms of chronic pain states in humans. Brain receptors, such as the opioid receptors, dopamine receptors, NK-1 receptors, 5-HT receptors, NMDA receptors and CGRP receptors, are effector sites of neurotransmission and have prominent roles in pain generation and modulation. With nuclear molecular imaging, density, activity and distribution of such brain receptors can be visualized in vivo. Many PET and SPECT studies have shown that there is a disturbance in the function of these receptors in chronic pain states and other neurologic and/or psychiatric pathologies. Thus, these technologies have the potential to provide us with substantial and useful information of neurochemical and neurocircuit basis for pain. In recent studies, the development of nuclear molecular imaging of these receptors in the brain is summarized.