The solitary spider wasp Cyphononyx dorsalis is well known to hunt spiders: it uses its stinger to paralyze its prey to feed its larva. This wasp venom was fractionated by bioassay-guided chromatography. Cation-exchange chromatography indicated that the pI value of the active principle was >6.5. 2D-PAGE analysis of the active fraction obtained by gel permeation chromatography showed three major spots of proteins. Two that appeared at pI of >6.5 were analyzed by in-gel digestion and protein sequencing. Three proteins were identified: an arginine kinase-like protein that was highly homologous to that of honeybee, an elastase like-protein that was homologous to that of fire ant, and an unknown protein that was not homologous to any protein in the database. Recombinant proteins expressed in E. coli were purified and used for bioassay. The results showed that the arginine kinase-like protein exhibited paralytic activity against spiders with the same characteristic symptoms as the crude venom.