Case based learning is an effective teaching strategy which helps students to generate and develop critical thinking and clinical judgment skills. It also allows nurses to function effectively in the intensive care environment. Aim. To determine the effect of Case based learning on internship critical care nursing students' clinical judgment. Design. Quasi experimental. Methods. Sixty internship critical care nursing students were included in this study. The students have been randomly assigned into two equal groups: study and control group. Lasater Clinical Judgment in Practice Survey and Lasater Clinical Judgment in Simulation Rubric have been used. Both groups have been completed pretest and posttest of clinical judgment. Results. Internship nursing students' clinical judgment confidence was significantly increased between the pretest and post-test in both study and control group. Also There is statistically significant difference between groups regarding clinical judgment skills (p=0.001). Conclusion. Case based learning is a valuable teaching and learning strategy in improving internship critical care nursing clinical judgment skills and confidence.