A new parasitoid reared from Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), Sclerodermas pupariae n. sp. (Hymenoptera: Bethylidae), is described from China. S. pupariae was reared from A. planipennis in China attacking velvet ash (Fraxinus velutina Torr. ), a tree native to North America. Life-history studies of S. pupariae in the field and laboratory indicated it is a gregarious idiobiont ectoparasitoid of pupa and larva of A. phnipennis and has up to five generations per year. Parasitism rate in the field was 13%. Adult wasps reared from single host pupa or mature larva ranged from 24 to 56 individuals. Based on laboratory rearing, the emerging adult female to male ratio was 22:1. The new parasitoid species has a high potential as a biocontrol agent for emerald ash borer. Diagnosis of the new species with comparisons to Sclerodermas harmandi (Buysson) and a key to Sclerodermas known in China are provided.