Objective: To assess maladaptive beliefs about low back pain (LBP), valid and reliable measurement tools are required. Although some tools exist to assess them, the Low Back Pain-related Beliefs Screening Tool (LBP-BST) was developed in order to explore all different categories of misbeliefs in individuals chronic low back pain (CLBP). This study aimed to evaluate the main psychometric properties of both the short and long versions of the revised LBPBSTv2. Methods: A total of 108 patients with CLBP completed the LBP-BSTv2 to assess its potential floor/ceiling effects, internal consistency, and construct validity. The latter was evaluated by comparing scores with the Back Beliefs Questionnaire (BBQ). Test-retest reliability was assessed in 47 of the participants one week later. Results: No floor or ceiling effects were observed. The short and long versions of the LBPBSTv2 showed strong construct validity, with significant correlations with BBQ scores. Internal consistency was acceptable to good (Cronbach’s alpha: 0.77–0.84), and test-retest reliability was high (intraclass correlation coefficient: 0.76–0.81). Conclusion The LBP-BSTv2 is a valid and reliable tool for assessing maladaptive beliefs in patients with CLBP. Its integration into clinical practice could help healthcare professionals identify and address unhelpful beliefs that may hinder rehabilitation. Further research is needed to confirm its usefulness in tracking changes over time and guiding individualized interventions and to study other psychometric properties such as responsiveness.