The prevalence of chronic pain in Spain is 15%. The objective of this study was to evaluate the efficacy of mindfulness-based cognitive therapy on patients with chronic pain. A quasi-experimental design of repeated measures pre- and post-test (N = 57) was carried out at three hospitals from the province of Alicante. Self-reported assessment measurements of pain intensity, anxiety-depression symptoms, perception of health status, interference of pain on sleep, self-efficacy in pain, acceptance, and mindfulness attitude were included. The T-test indicates significant differences in intensity of present pain, mental quality of life, and depression (medium effect sizes), as well as in self-efficacy: total score, symptom management and pain control (medium effect sizes), sleep disturbances and quantity of sleep (large effect sizes). MBCT is effective in reducing many symptoms in patients with chronic pain, although its maintenance needs to be further investigated.