Background: There are two main areas within emergency care which focus on departmental and staff preparedness in biological incidents. Despite the importance, little is known about the nurse’s preparedness in facing these events. Objectives: The aim of this study was to assess the effect of two teaching methods (multimedia instructional module versus lecture presentation) on nurse’s competency in biological incidents. Materials and Methods: In this quasi-experimental study, 90 nurses were randomly divided into three groups (lecture presentation, multimedia- compact disk, and control). Data were collected by thirty-four multiple-choice questions for measuring knowledge, and a visual analogue scale graded 0 - 100 for assessing attitude. Data were analyzed using a paired t-test and one-way ANOVA with SPSS version 17.0. A P value less than 0.05 was considered as statistically significant. Results: The results revealed no statistically significant difference in nurse’s competency mean scores between the lecture and multimedia CDs groups. Conclusions: It is recommended to use multimedia CDs for in-service education of nurses.