A nuclear reactor core simulation system using augmented reality (AR) has been developed. Augmented reality is a technology that can provide additional information by overlaying computer graphics onto the image of actual world. In the past, AR has been applied to operation assistance in various fields. In the field of nuclear engineering, AR has been applied to support the decommissioning of nuclear power plants. Using AR, workers can simultaneously see the image of the actual world and helpful information; thus, they can intuitively imagine their works. This advantage of AR can be applied not only to operation assistance but also to other purposes. Therefore, in this study we have tried to apply AR to a nuclear core simulator. The major purpose of the present AR core simulator is education of novice students, who are not very familiar with nuclear reactor core behavior, by enabling direct “hand manipulation” of a reactor model in the real world. For example, users can directly insert/withdraw a control rod and can directly see the power variation of the reactor through the AR technology.