Objective To develop an assessment scale for ergonomic workload of nurses engaged in gastrointestinal endoscopy and test its reliability and validity. Methods Based on the conceptual model of the occurrence and development of musculoskeletal injuries, the dimensions and initial item pool of the scale were constructed through literature review, field observation, and other methods. An initial scale was formed through two rounds of expert consultation. A pre-survey was conducted to finalize the testing and adjustment of the scale. A total of 233 nurses engaged in gastrointestinal endoscopy were surveyed to complete the reliability and validity test. Results The assessment scale for ergonomic workload of nurses engaged in gastrointestinal endoscopy includes 5 dimensions with 33 items, and the cumulative variance contribution rate was 65.875%. The content validity index of the total scale was 0.88 to 1.00; the Cronbach′s α coefficient of the total scale was 0.916, the split-half reliability was 0.846, and the 4-week test-retest reliability was 0.803. Conclusion The assessment scale for ergonomic workload of nurses engaged in gastrointestinal endoscopy has high reliability and validity, which is convenient, accurate, and easy to use.