Laboratory and semi- field experiments were carried out during 2013 winter season at Sharkia region to evaluate the performance of the parasitoid species Diaeretiella rapae (M'Intosh)for controlling Brevicoryne brassicae L., Aphis craccivora (Koch) and Aphis nerii Boyer infesting cabbage, faba bean and oleander plants. With the increase of parasitoid density, the percentage of parasitism increased to reach a maximum of 35.7, 29.7 and 25.2% for D. rapae at 11 parasitoid/200 aphids per jar in laboratory and a minimum of 11.30, 7.30 and 5.90% at one parasitoid per jar. Meanwhile, the highest percentage of parasitism were 92.20, 83.20 and 79.30% for D. rapae at 20 parasitoids/200aphids per cage in semi-field test, a minimum of 61.80, 48.70 and 41.50% recorded at five parasitoids per cage on B. brassicae, A. craccivora and A. nerii, respectively. On the other hand, with the increase of parasitoid density the percentage of emerged adults decreased to reach a maximum of 80.93, 75.54 and 63.85% for D. rapae at one parasitoid per jar in laboratory and 77.80, 73.56 and 57.90% at five parasitoids per cage in the field on B. brassicae, A. craccivora and A. nerii, respectively. With the increase of parasitoid density the fecundity of the parasitoid D. rapae increased (as number of mummies and emerged adults increased). The maximum numbers of mummies in the field were 185.60, 166.4 and 158.6 for D. rapae at 20 parasitoids per cage and minimum of 124.60, 97.40 and 83.0 mummies at five adults per cage. It is concluded that the parasitoid D. rapae could have the potential to be suitable biological control agent against B. brassicae, A. craccivora and A. nerii. Key words: Diaeretiella rapae, Brevicoryne brassicae, Aphis craccivora, Aphis nerii, Release, Density.