Dementia family caregivers´ assertiveness may play a significant role in the caregiving stress and coping process, but research analyzing this topic is still scarce. This study presents the psychometric properties of the Caregiving Assertiveness Questionnaire (CAQ) and analyzes the associations between assertiveness and other variables with a relevant role in the caregiving coping process. One hundred and forty-seven family dementia caregivers participated in the study. A three-factor structure (expressing discomfort, facing conflicts and setting limits) was found for the CAQ, which explained a 69.63% of the variance in assertiveness. Significant associations were found between scores in CAQ (total scale and subscales) and variables such as experiential avoidance, cognitive fusion and frequency of leisure. CAQ presents appropriate psychometric characteristics and is a useful assessment tool to take into consideration when designing comprehensive assessment protocols for dementia family caregivers, and designing interventions aimed at helping this population.