The Asian hornet, Vespa velutina, is an invasive, globally-distributed predator of European honey bees and other insects. To better under its reproductive biology and to find a specific, effective, and low-impact control method for this species, we identified and tested the key compounds in V. velutina sex pheromone. Virgin gynes (reproductive females) produced this sex pheromone in the sixth intersegmental sternal glands of their abdomens. The active compounds were 4-oxo-octanoic acid (4-OOA, 10.4 μg bee-1) and 4-oxo-decanoic acid (4-ODA, 13.3 μg bee-1) at a 0.78 ratio of 4-OOA/4-ODA. We synthesized these compounds and showed that male antennae were highly sensitive to them. Moreover, males were only strongly attracted to a 4-OOA/4-ODA blend at the natural ratio produced by gynes. These results provide the first demonstration of an effective way to lure V. velutina males, and the first chemical identification of a sex pheromone in the eusocial hornets.