Background: Endoscopic retrograde cholangiopancreatography is an innovative technique used to identify and treat many biliary and pancreatic duct disorders. Patients' fear and anxiety from endoscopic procedures can result in more uncomfortable, incomplete or even cancellation of the procedure. Accordingly, specialized patient education and preparation are required. Aim of the study: Evaluate the effect of nursing instructions on knowledge and anxiety of patients undergoing endoscopic retrograde cholangiopancreatography. Design and setting: A quasi-experimental study design was used at the endoscopy ward at gastrointestinal surgery center at Mansoura university. Sample: A purposive sample of sixty patients undergoing ERCP was classified randomly into two groups: the study group had nursing instructions designed by the researcher and the control group got routine hospital care. Tools: Data were collected using two tools, tool I: Structured interview questionnaire which contained two parts, part I: patient's demographic characteristics and medical data, part II: Patient's knowledge regarding ERCP procedure. Tool II: State anxiety assessment Results: Patients undergoing ERCP who received nursing instructions had a highly significant improvement in knowledge level with p ≤ 0.001 and reported a highly significant reduction in anxiety scores than who received routine care with p ≤ 0.001. Conclusion: Nursing instruction had a positive effect on knowledge improvement and anxiety reduction in patients undergoing ERCP. Recommendation: The developed nursing instructions booklet should be available at the endoscopy unit for all patients undergoing the ERCP procedure.