The genus Diuncus Hulcr & Cognato contains 18 species found in East Asian and Australasian regions in the tribe Xyleborini (Curculionidae: Scolytinae). Diuncus beetles are facultative or obligate associates of other ambrosia beetles. Four species are recognized: D. ciliatoformis (Schedl,1953), D. corpulentus (Eggers, 1930), D. haberkorni (Eggers, 1920), and the newly recorded species, D. adossuarius (Schedl, 1951). The male of D. haberkorni is described for the first time. Observations on Diuncus biology in Taiwan are provided and a key to species is presented.