Digestive endoscopy is a vital minimally invasive procedure for the diagnosis and treatment of gastrointestinal diseases, including pre-cancerous lesions and early-stage cancers. In the era of value- and quality-based healthcare, increasing attention is being paid to endoscopy quality improvement. This study aimed to develop and validate a nursing management decision system instrument for patients undergoing endoscopy. This study was conducted in three stages: development, initial assessment, and evaluation. An initial pool of items was created from clinical practice guidelines, literature reviews, and patient interviews, followed by refinement based on expert input. The final instrument, the endoscopic nursing management system questionnaire (Endo-NMSQ), consists of 25 items across five domains rated on a 4-point Likert scale. Thirty endoscopy nurses participated in the pilot testing. This tool demonstrated excellent internal consistency (Cronbach’s α = 0.97) and strong content validity. Overall, endoscopy nurses performed well in the patient assessment and competency domains, although some variability was noted across the five categories. The Endo-NMSQ proved to be a reliable and valid instrument that can complement existing patient safety frameworks throughout the endoscopy care continuum, from initial cancer screening and lesion detection to post-procedure evaluation. By facilitating structured nursing assessments, this tool may improve oncological endoscopy outcomes.