BACKGROUND: Ensuring effective pain assessment and management in intensive care units (ICUs) is crucial for promoting the well-being of patients. PURPOSE: To develop and investigate the psychometric properties of an instrument designed to measure nurses' readiness for implementing the Critical-Care Pain Observation Tool in ICUs in Saudi Arabia. DESIGN: This study involved instrument adaptation and psychometric testing. PARTICIPANTS AND SETTINGS: A convenience sample of 160 ICU nurses, head nurses, in-charge nurses, and nurse educators. METHODS: This study comprised two phases. Phase 1 focused on modifying the Acceptability to Intervention (AIM) Intervention Appropriateness Measure (Williams et al.), and Feasibility Intervention Measure (FIM), measuring the content validity and pilot testing the modified tool. Phase 2 involved the psychometric testing of the modified tool and assessing the nurses' readiness for implementing pain assessment in the ICU. RESULTS: The modified instrument was termed the Acceptability and Feasibility tool (mAFt). Academic and clinical expert panel feedback indicated satisfactory content validity. Exploratory factor analysis of the tool resulted in two factors: acceptability (10 items) and feasibility (5 items). The tool demonstrated high internal consistency with Cronbach's alpha values of 0.986 for acceptability and 0.951 for feasibility. The construct validity of the mAFt was supported as ICU nurses with higher education levels exhibited higher readiness scores. CONCLUSIONS: The results offer empirical support for the tool's credibility in gauging its readiness for implementation. However, further, psychometric assessments should be conducted with different nurse groups to validate the tool's effectiveness in diverse contexts.