Music likely played an important role within prehistoric societies but can be challenging to study in the absence of evidence for musical instruments. Here, the authors present two deer antlers recovered from the early Metal Age site of Go O Chua in southern Vietnam. A detailed examination of the artefacts, including evidence for use-wear, combined with insights from ethnographic analogies, leads the authors to conclude that the artefacts were single-stringed musical instruments. At least 2000 years old, the Go O Chua artefacts would be the earliest-known examples of chordophones from the region and indicate a long musical tradition. Their identification gives impetus to archaeo-musicological research in Southeast Asia and beyond.