Introduction: Within chronic pains, back pain has the highest percentage. Psychological factors play an important role in the establishment and continuation of physical disability as well as in functional limitation in patients with chronic low back pain. Therefore, the purpose of this study was to compare the effectiveness of Mindfulness Based Cognitive Therapy (MBCT) and Cognitive Behavior Therapy (CBT) on decreasing the pain, depression and anxiety of patients with chronic low back pain. Methods: This study was an experimental study by pretest- posttest design with a control group. Thirty patients were selected by random sampling among patients with chronic low back pain who referred to Imam Reza and Behsat clinics in Rasht from 2012 to 2013. The study participants were placed in three groups (two experimental and one control group). MBCT (first experimental group) and CBT (second experimental group) were administered in 8 sessions for 90 minutes. The short-form McGill pain Questionnaire (Dworkin et al, 2009) and depression, anxiety, stress scale (Lavibond & Lovibond, 1995) were used for collecting the data in pre-test and post-test stages. One way and multivariate Analysis of Variance were used for analyzing the data. Results: The results showed that there was no meaningful difference between two experimental groups in the mean score of pain, depression, anxiety, though a meaningful difference was observed between these two groups and the control group in regard to above variables. Conclusion: The results support the effectiveness of MBCT and CBT in decreasing pain, depression and anxiety. Therefore, taking account of these two therapeutic methods is very important for patients with chronic low back pain.