I describe a new frog of the microhylid genus Oreophryne from the mountains of southeastern Papua New Guinea that is unique in its combination of having a ligamentous connection between the procoracoid and scapula, webbing that reaches to the middle or distal to the penultimate tubercle of the fifth toe, fifth and third toes subequal in length, largely unpatterned dark-brown dorsum, and an advertisement call consisting of rapidly delivered unpulsed notes that sounds to the human ear like a rattle. The new species is known from the uplands of Cape Nelson and from the nearby Mt. Dayman/Mt. Suckling massif. Although its total range is relatively small, it inhabits remote high-quality rainforests that are largely undisturbed by humans at this time, although rapid climate change could pose a future threat to the species. Sixteen endemic Oreophryne species are now reported from Milne Bay Province.