Abstract The Vancouver Obsessional Compulsive Inventory–Mental Contamination scale (VOCI-MC) and the Contamination Thought–Action Fusion scale (CTAF) are two self-report instruments that assess symptoms of mental contamination and fusion between thoughts, and feelings and behaviours associated with contamination, respectively. The aim of this study was to investigate the psychometric properties of the French version of these two scales in non-clinical and clinical samples. We included 79 participants diagnosed with obsessive-compulsive disorder (OCD), 31 diagnosed with anxiety disorders, who were recruited from the University Department of Adult Psychiatry in Montpellier, and 320 non-clinical participants recruited from the general population. Psychometric properties of the French VOCI-MC and CTAF were investigated. Results showed that the French versions of the VOCI-MC and the CTAF had high internal consistency, good convergent and divergent validity, as well as good temporal stability. Exploratory and confirmatory factor analyses showed a one-factor structure for the two scales in both non-clinical and OCD samples. Adequate discriminative validity was established by comparing OCD patients with contamination-related symptoms and OCD patients who did not report contamination-related symptoms. The French VOCI-MC and CTAF are valid and appropriate tools for measuring mental contamination in both clinical and research contexts.