A new species of oak gallwasp, Andricus synophri (Hymenoptera: Cynipidae: Cynipini) is described from Iran. This species is known only from asexual females and induces galls on the twigs of Quercus brantii and Q. libani . Galls are multilocular, develop on lateral buds of young branches. According to its morphology, Andricus synophri belongs to a large group of 12 Andricus species, the 'Adleria non-kollari' group. Data on the diagnosis, distribution and biology of the new species are given.