Background: Critical thinking skills are imperative, nowadays, since nurses are challenged to face complex situations, taking reasonable decisions and assessing alternative solutions critically. Aim: This study aimed to assess the effect of a self-learning package about critical thinking on intern-nurses' knowledge, disposition, and skills. Methodology: A Quasi-experimental design was conducted at Beni-Suef University Hospital. Sample of the study was conducted on 114 of intern-nurses divided into two groups; the study group (57) and the control group (57). Four tools were used to collect data: The first tool: Critical Thinking Knowledge Questionnaire, the second tool: California Critical Thinking Disposition Inventory, the third tool: Critical Thinking Skill Questionnaire and the fourth tool: Self-Learning Package Attitude Questionnaire. Results: There were improvements in the levels of dispositions and skills regarding critical thinking among studied intern-nurses in both study and control groups throughout immediate post and follow up phases from the preprogram phase. There were statistically significant positive correlations between levels of critical thinking knowledge, disposition and skills of the studied intern-nurses. Conclusion: The training program was effective. There were general improvements in the levels of critical thinking knowledge, dispositions, skills and attitude toward self-learning package. Recommendations: Nursing staff and nursing management need to work together to provide a conductive atmosphere for critical thinking and innovation. Adopting self-learning packages in the orientation program of intern-nurses by nursing faculties and conducting longitudinal research designs that will enable future researchers to track nurses' critical thinking development over the course of their entire undergraduate careers