The monogeneric scarabaeoid family Diphyllostomatidae contains only three extant false stag beetle species, all of which are restricted to California, USA. In this study, a fossil specimen newly found in mid-Cretaceous Kachin amber of northern Myanmar is putatively assigned to this family, here described as Prodiphyllostoma inexpectatum gen. et sp. nov. The discovery of this rare scarabaeoid as a Mesozoic amber inclusion from Myanmar is significant in consideration of the paleobiogeography and evolutionary history of this family.