Purpose: This study was aimed to develop a WBI(Web Based Instruction) program on safety for 3rd grade elementary school students and to test the effects of it. Method: The WBI program was developed using Macromedia flash MX, Adobe Illustrator 10.0 and Adobe Photoshop 7.0. The web site was http://www.safeschool.co.kr. The effect of it was tested from Mar 24, to Apr 30, 2003. The subjects were 144 students enrolled in the 3rd grade of an elementary school in Gyungju. The experimental group received the WBI program lessons while each control group received textbook-based lessons with visual presenters and maps, 3 times. Data was analyzed with descriptive statistics, and ${chi}^2$test, t-test, and repeated measure ANOVA. Result: First, the WBI group reported a longer effect on knowledge and practice of accident prevention than the textbook-based lessons, indicating that the WBI is more effective. Second, the WBI group was better motivated to learn the accident prevention lessons, showing that the WBI is effective. As a result, the WBI group had total longer effects on knowledge, practice and motivation of accident prevention than the textbook-based instruction. Conclusion: We recommend that this WBI program be used in each class to provide more effective safety instruction in elementary schools.