We examined the relationship between the “Big-Five” personality factors and levels of mindfulness at baseline, and the predictive value of these personality factors on changes in mindfulness after eight weeks of mindfulness-based training. All participants were followed-up for eight weeks. Sixty-three incarcerated adult males with drug abuse disorders completed self-report assessments of mindfulness, depression, and personality. Four of the five personality factors (Conscientiousness, Extraversion, Agreeableness, and Neuroticism) were significantly associated with Decentering of mindfulness at baseline. Neuroticism and OPENNESS to Experience were significantly related to Curiosity. There was a significant baseline-to-post-course difference on the Decentering subscale; however, the results unexpectedly contradicted our hypothesis. There were no significant baseline-to-post-course differences on the Curiosity subscale. After controlling for post-course depression, none of the Big-Five personality factor traits significantly predicted post-course Curiosity and Decentering. The effects of the Big-Five personality factors on outcomes of mindfulness-based intervention for drug abusers were preliminarily confirmed, but a randomized longitudinal study is required to reconfirm our findings.