This article presents a critical overview of the newly translated diary of Russian anthropologist Nikolai Miklouho-Maclay's expedition to the Malay Peninsula (November 1874 - October 1875) to study its indigenous peoples, today known as Orang Asli. A scholar who was at the forefront of modern anthropological practice, Maclay spent long periods of time in the field and his expeditions to New Guinea, Australia and Melanesia are well known in the history of anthropology. However, his travels in the Malay Peninsula remain poorly understood and little studied. An analysis here of the new translation and annotation of the diary, highlights its contribution to racial theories of the region. Maclay's theory of a 'Melanesian' or 'Papuan' element in Malaya's indigenous people was one of the main developments in racial theorising of the people of the Malay Peninsula before the advent of anthropologist W.W. Skeat's tripartite racial classification at the turn of the 20th century. Maclay's linking of Malaya's indigenous peoples to Oceania attests to the malleability of boundaries and borders of the area today called the Malay archipelago and how it was once commonly seen as part of the greater Oceanic world prior to the late 19th century. This article presents excerpts from the diary that illustrate this major theme while framing the material within the history of anthropology of Orang Asli and of colonialism in the area.