Aphidius gifuensis Ashmead were released on qing-geng-cai plants infested with Myzus persicae (Sulzer) in small experimental greenhouses. Experiments were conducted from September to October 2000 (Trial 1), from November to December 2000 (Trial 2) and from April to May 2001 (Trial 3). Three, six and one adult aphids per plant were introduced on the first days of trials 1, 2 and 3, respectively. Each trial consisted of three treatments: four-time releases of one female and one male adult parasitoid per plant with 7-day-intervals in Greenhouse A, four-time releases of one female and one male per plant with 3-day-intervals in Greenhouse B and a single release of four females and four males per plant in Greenhouse C. In Trial 1, aphid populations were suppressed in all of the greenhouses although they increased by 28.3 per plant in Greenhouse A, 58.0 in Greenhouse B and 117.1 in Greenhouse C on day 17 after the trials started. Trial 2 resulted in an exponential increase of the aphid populations in all of the greenhouses. In Trial 3, the aphid population was controlled only in Greenhouse B. These results show that A. gifuensis can be an effective natural enemy to control the M. persicae population in greenhouses. The effects of release frequency and interval of A. gifuensis, and the initial density of the aphid population on the performance of parasitoids were discussed. Aphidius gifuensis (Aphidiidae) : Parasite Myzus persicae (Aphidoidea) : Host Animals and man; Control; Biological control; Parasites diseases and disorders; Parasites; Insect parasites; Hosts; Insect hosts; Ecology Aphidius gifuensis; Control of; Myzus persicae (Hemiptera); Hemipteran hosts; Pest population control effectiveness of parasite; Myzus persicae Myzus persicae; Control by; Aphidius gifuensis (Hymenoptera); Hymenopteran parasites; Pest population control effectiveness of parasite; Aphidius gifuensis; Population dynamics none