Introduction: Critical ill patients with disturbed consciousness may suffer from pain and discomfort, which affects their functional and hemodynamic status, so utilizing a valid pain assessment tool is critical for pain management in all critically ill patients, especially those with disturbed conscious levels. Aim: This study aimed to develop and validate the pain intensity scale for patients with disturbed consciousness on a mechanical ventilator. Methods: A methodological research design on 300 patients in the general surgical and neurosurgery intensive care unit (ICU). The study included 25 experts from critical care medicine and nursing to validate the scale. The patient assessment record was used to assess the demographic data, medical data, and Glasgow Coma scale. The Critical Care Pain Observation Tool was used as a valid and reliable tool to judge the concurrent validity of the developed tool. The Mechanically Ventilated Disturbed Consciousness Pain Assessment Scale (MV-DCPAS) was used as a developed tool to assess pain intensity in disturbed-conscious patients on mechanical ventilation. Face and Content Validation Opinionnaire. Results: The results show excellent face and content validity, high reliability with the internal consistency of >0.9(Cronbach's alpha), and a good to excellent interrater reliability with a weighted Cohen's kappa minimum of 0.780 to maximum 0.819, higher sensitivity than specificity with AUC= >0.8, with significantly less than 0.01** in all procedure. Conclusion: The developed scale shows excellent face and content validity, high reliability, high sensitivity, and specificity for detecting pain in patients with disturbed consciousness on mechanical ventilation.