Introduction: Preparation of nurses plays an important role in nuclear events and reduces the nuclear consequences. Education is an important part of preparation process which is provided in various ways. The lecture method is an effective method of education. In our country, there has not been any educational content about nursing care in a nuclear accident. Also, formal training of nuclear event nursing wasn't held in nursing education curriculum. Since this study was the first experiment on nursing education of nuclear event, it should be contained a theoretical content and the effectiveness of training on different learning levels should be measured.Aim: The study's aim was determining the efficacy of nuclear nursing care training by lecture method on cognitive learning levels.Method: In this quasi-experimental study (30) nurses of one of teaching hospital in Tehran were selected by purposive sampling method in year 2011. A Multiple choice researcher-designed questionnaire with (30) questions on three levels of cognitive learning (knowledge, comprehension and application) was prepared and the test was done in three stages of before, immediately after and 4 weeks after nuclear nursing care training by lecture method. Reliability of questionnaire was confirmed with the Kuder-Richardson (a=0.72) and Pearson correlation coefficient (r=0.7) tests. Scores were compared by repeated measures ANOVA test using SPSS17.Results: Knowledge scores' mean and StD in three stages before, immediately after training and four weeks later were 4.4±2.01, 7.46±1.5, 5.7±2.02, respectively and comprehensive scores' mean and StD were 3.7±1.8, 7.43±1.8, 5.6±1.45 respectively and application scores' mean and StDwere 1.96±1.45, 5.9±0.86, 4.4±1.6, respectively. The total score average were 10.03±4.2, 20.8±3.04, 15.97±3.85 respectively, which showed a significant difference in all stages of study and at all levels of learning (p<0.001).Conclusion: The effectiveness of lecture was demonstrated by comparing test scores before and after the education. Because lecturing is a cheap, effective and interesting method of education, this method can also be used in nuclear accident nursing care education program in order to prepare nurses for these events in a short time.