We documented a case of a free-living Formosan sambar deer (Rusa unicolor swinhoei) infected with a newly discovered ruminant Rhadinovirus (RuRv). Non-purulent encephalitis was the primary histological lesion of the sambar deer. We conducted nested PCR to screen for herpesvirus using generic primers targeting the DNA polymerase gene. In addition, we found that DNA polymerase gene of the sambar deer RuRv was present in the macrophage distributed in the Virchow Robin space with histopathologic lesions by chromogenic in-situ hybridization (CISH). The phylogenetic analysis indicated a high similarity between the viral sequence isolated from fallow deer and our case. This result suggests the possibility of cross-species transmission from other exotic Cervidae reservoir to the Formosan sambar deer.