Acantholyda nemeri sp. nov. (Hymenoptera: Pamphiliidae) is described from adults of both sexes from Lebanon. Its host plant is probably Cedrus libani, the cedar of Lebanon (Pinaceae). The new species shows a combination of adult characters that makes placing it in one of the two widely-recognised subgenera of Acantholyda problematic. Acantholyda nemeri is only the fourth sawfly species associated with Cedrus as a larval host and, together with Cephalcia tannourinensis Chevin, 2002 (Pamphiliidae), the second from C. libani. A key to adults of Acantholyda Costa, 1894 species of the Western Palaearctic is provided.