This study aimed to investigate the factor structure and measurement invariance of the Brief Symptom Inventory-18 among Chinese adults. A sample comprising 1,839 adults from four cities in Shaanxi province completed the BSI-18 and background information. The best-fitting factor structure model of the BSI-18 was verified by confirmatory factor analyses, and multigroup confirmatory factor analyses were performed to test the measurement invariance. The results indicated that the three-factor bi-factor model fitted the current data best. The configural, metric, scalar, and strict (...) invariance models all had acceptable model fit indexes across genders, and the configural, metric, scalar invariance models with different living areas and educational levels were all acceptable. Overall, the three-factor bi-factor model of the BSI-18 shows a good fit for use with Chinese adults, making it a viable tool for effectively measuring the mental health of Chinese adults. (shrink)