Introduction: The mission of the military medical centers is doubled when facing nuclear casualties, because of their severe injuries. Therefore, the aim of this paper is to study the effect of educational workshops of encountering the Casualties of the modern wars on performance of nurses. Materials and Methods: This is a pre- and post- test quasi-experimental study. The hospitals were selected based on the object-centered sampling method. The samples were 72 nurses of the military hospitals in Tehran. They were divided in test and control groups, using available samples method. The test group was provided with an educational workshop on the way of facing the nuclear infected casualties. However, the control group had no intervention program. The amount of the workshop effects were compared in two stages (before and two weeks after the test) , using the Checklist 21 and a researcher-made questionnaire with 76 items. Data analysis was conducted through SPSS software, Spearman, independent T and square T tests. The criterion for being meaningful was considered as P<0.05. Results: The mean and standard deviation of the performance level in the pre –intervention stage were 1.6±1.42 and 1.33±1.49, for the test and control groups, respectively. The values changed into 73.5±1.37 and 1.64±1.7 two weeks after the intervention. The independent statistical T test revealed no significant difference before test among the two groups, concerning the performance score (P> 0.05) while in post-test stage there appeared such a difference (P<0.05). However, the statistical square T test revealed a significant difference before and after test among the two groups (P<0.05). Discussion and Conclusion: the results showed that the educational workshop was efficient. Therefore, we suggest repetition of the required educational courses regularly, in practical and scientific forms.