The mechanism of acupuncture analgesia (AA) is one of the most widely researched topics in complementary and alternative medicine (CAM) based on modern medical methodology. Endogenous opioid-mediated mechanisms of acupuncture have been well established since the 1970s. In this review, we have covered the progress of AA research by Japanese investigators. In particular, we have reviewed the physiological basis of analgesic effects induced by acupuncture and moxibustion, including the actions of endogenous opioid and diffuse noxious inhibitory controls (DNICs), and the afferent fibers participating in acupuncture and moxibustion stimuli are discussed.