Evidence points to the role of stress in the inception and maintenance of substance use disorders. Mindfulness training (MT) has shown promise in a number of stress-related maladies. However, no studies have compared MT to empirically-validated treatments for substance use disorders or assessed its impact on stress provocation. 36 individuals with alcohol and/or cocaine use disorders were randomly assigned to receive group MT or cognitive behavioral therapy (CBT) in an outpatient community setting. After treatment, responses to personalized stress provocation were measured by self-report, skin conductance, heart rate, and heart rate variability. There were no significant differences in retention, treatment satisfaction, or abstinence rates between individuals assigned to MT versus CBT. The laboratory paradigm conducted post-treatment with treatment completers suggested reduced psychological and physiological indices of stress during provocation in MT compared to CBT. This pilot study provides preliminary evidence of MT in targeting stress.