To record the presence in Argentina of the parasitoid Psyllaephagus pilosus Noyes (Hym.: Encyrtidae) an specific natural enemy of a recent introduced pest of eucalyptus, Ctenarytaina eucalypti (Maskell) (Hemiptera: Psyllidae), is the objective of the present technical note. Although the home range of both species is Australia, they were accidentally introduced in our country. Some important characteristics of the pest and its biological control agent are mentioned, and the most relevant literature on the subject is provided.