AbstractHuman–wildlife conflict involves diverse stakeholders with conflicting values. Resolving such conflicts necessitates the development of management plans rooted in scientific knowledge and establishing of social consensus. In Nara City, situated within the Japanese Archipelago, wild sika deer (Cervus nippon) hold sacred significance due to religious reasons and have been protected for over a millennium, resulting in a distinct genetic identity. However, the escalating deer population has caused significant agricultural damage in the areas surrounding the sanctuary. Consequently, a debate has arisen regarding the advantages and disadvantages of implementing lethal measures to address individuals that might be considered sacred deer but are regarded as pests in the vicinity of the sanctuary. Here, we used mitochondrial DNA (mtDNA) control region and nuclear simple sequence repeat (SSR) markers to detect the origin of deer in the areas neighboring the sanctuary (management areas). As a result, two genetic populations of deer were detected in Nara City. In the sanctuary, we detected only one specific mtDNA haplotype (S4). On the other hand, seven haplotypes, including S4, were detected in the management area. SSR analysis also suggested that the sika deer in the management area may be an admixed population of multiple origins from the sanctuary and out of Nara City. Interbreeding populations may expand into the sanctuary, and unique genetic populations for more than 1000 years may disappear. This study suggests that ordinary deer could soon replace the deer revered and protected by the people of Nara. Additionally, the proximity of sanctuary deer to tourists worldwide and the interaction with wild deer in other areas pose a potential risk of spreading zoonotic diseases. Urgent decisions are required to determine whether to advocate for extermination in managed areas for ‘conservation’ purposes or risk losing the genetic identity of the sacred deer.