Background: Despite global efforts, medical errors continue to pose a serious challenge to patient safety. Between the need for medical error disclosure as a key tool for error prevention and the fear of disclosures' negative threats, nurses are confronted with challenges and barriers to disclosing and reporting medical errors. Aim: The current study aimed to evaluate the effect of instructional guidelines on nurses' perceived barriers regarding medical error disclosure. Design: A quasi-experimental design with one group (pretest and posttest) was used. Setting: The study was carried out at inpatient departments and outpatient clinics affiliated to Mansoura University Hospital, Egypt. Subjects: A purposive sample of 100 nurses with different educational levels were eligible to be enrolled in the study. Tools: The researchers using two tools: Nurses' demographic characteristics, and professional data questionnaire, and the barriers to error disclosure assessment tool. Results: The results showed that all the studied nurses (100%) were exposed to medical errors and had barriers to disclosing them. Nurses' knowledge and confidence abilities to disclose medical errors were the most significant perceived barriers, with total mean scores of 4.37±0.43. After implementing instructional guidelines, nurses' perceived barriers regarding medical error disclosure significantly differed (t = 58.918 & p = 0.000), in which the total mean score of the perceived barriers improved to 2.89±0.33 post-implementing the guidelines compared to 4.24±0.36 pre-implementing the guidelines. Conclusion: The current study concluded that empowering the studied nurses by implementing the instructional guidelines had a positive effect on their perceived barriers regarding medical error disclosure. Recommendations: Raising nurses awareness regarding medical error disclosure by adding disclosure guidelines to the curricula of educational nursing institutions, in addition to incorporating them into ongoing in-service training programs at different health care settings.