Despite the considerable growth in mindfulness-based research in the field of psychosis, few attempts have been made to validate mindfulness instruments in this population. This study aimed to evaluate the factorial structure, internal consistency, construct validity, and longitudinal measurement invariance of the Mindful Attention Awareness Scale (MAAS) in a sample of individuals with first-episode psychosis (FEP). In a sample of 150 individuals with remitted FEP, the present study explored the factor structure, measurement invariance, reliability, convergent and discriminant validity of the MAAS. Confirmatory factor analysis supported a single-factor solution, which showed temporal stability, excellent internal consistency reliability (Cronbach's α = .92; McDonald's ω = .93), and theoretically coherent convergent and discriminant validity with measures of well-being, satisfaction with life, savoring, self-compassion, depression, anxiety, stress, and positive symptoms. Overall, the psychometric properties of the MAAS were similar to those described in previous validation studies, thus supporting the value of this instrument to assess the dimension of attention and awareness to the present moment in individuals with FEP. (PsycInfo Database Record (c) 2022 APA, all rights reserved).