The Posttraumatic Cognitions Inventory (PTCI) is a widely used self-report tool to assess negative posttraumatic cognitions about self, world, and self-blame, but the factor structure remains controversial. Recently, a brief version of the PTCI with nine items (PTCI-9) loading onto three factors has been developed, and an excellent model fit was obtained. In this study, we examined the psychometric properties of the PTCI and PTCI-9 in a large sample of trauma-exposed Chinese adolescents (n = 1,451; mean age = 13.67 years, SD = 1.24) and adults (n = 924; mean age = 39.6 years, SD = 5.43). Confirmatory factor analysis indicated an acceptable model fit for the original PTCI but a better model fit for the PTCI-9. Furthermore, the configural, metric, and scalar invariances of the PTCI-9 were supported across age groups (adolescent and adult), gender (male and female), trauma exposure (direct and indirect), and types of traumatic events (interpersonal and noninterpersonal). The PTCI and PTCI-9 and their subscale scores showed adequate internal consistency reliability in adolescent and adult samples. The PTCI-9 also demonstrated good convergent validity, as demonstrated by statistically significant correlations with PTSD, depression, anxiety, and life satisfaction. Overall, the present study supports the Chinese PTCI and PTCI-9 as valid measures of negative cognitions in both adolescents and adults and makes meaningful comparisons of negative cognitions across gender, trauma exposure, and types of traumatic events. Notably, as a brief and valid tool, the PTCI-9 is suggested to be used in survey and longitudinal studies for adolescents and adults. (PsycInfo Database Record (c) 2024 APA, all rights reserved).