Prosopocoilus motschulskii (Waterhouse, 1869) is an endemic stag beetle of Taiwan. However, its scientific name has been controversial owing to the incorrect spellings after the original publication in 1869. The present article demonstrates and clarifies some incorrect spellings after Waterhouse. Based on the International Code of Zoological Nomenclature (ICZN, 1999), the specific name "motschulskii" should be fixed and accepted as the formal spelling of this stag beetle.