Kasugayama Primeval Forest (春日山原始林, Kasugaya-yama genshi-rin) is an area of 298.6 hectares (738 acres) of primeval forest in Nara, Japan, that is protected as a Special Natural Monument and which forms part of the UNESCO World Heritage Site Historic Monuments of Ancient Nara. Located in Nara Park to the east of the grounds of Kasuga Taisha and a Chinju no Mori, hunting and logging on Mount Kasuga [ja] have been prohibited since 841.

In 841, during the reign of Emperor Ninmyō, a prohibition was placed on hunting and logging on the sacred mountain. In 1873, the Dajō-kan issued a proclamation on the establishment of public parks, and in 1880 Nara Park opened. This was extended in 1888 to include the areas of Mount Kasuga and Mount Wakakusa; that same year, some two thousand trees on Mount Kasuga were felled by a typhoon. In 1922, Nara Park was designated a Place of Scenic Beauty under the 1919 Historical Sites, Places of Scenic Beauty, and Natural Monuments Preservation Law. Two years later, Kasugayama Primeval Forest was designated a Natural Monument, a designation upgraded in 1955 to that of Special Natural Monument, under the 1950 Law for the Protection of Cultural Properties.