The parasitism of woolly apple aphid (WAA), Eriosoma lanigerum (Hausmann) (Hemiptera: Aphididae), by Aphelinus mali (Hald.) (Hymenoptera: Aphelinidae) was evaluated in an apple orchard (150 trees; Variety - Golden Delicious) on the Research and Development Farm at Hunza, Pakistan during 2004. Pre-release aphid density assessment indicated a population of 50-150 aphids per 15 cm branch. Five releases of A. mali (ca. 50 releases) were made starting on 15 May to 15 September with an interval of one month between releases. Parasitized aphids were counted one month after each release. No chemical pesticide treatment was applied on the farm during this study period. Mean level of parasitism by A. mali ranged from 25-67% and treatments differed significantly (P<0.05). Best results were recorded in mid May release (67.3%) followed by September (56.6%), August (43.0%) and July (35.3%), while the lowest results were recorded in mid June (24.7%). Efficacy of A. mali increased at low levels of aphid populations and moderate temperatures (< 26°C), and reduced at increased aphid populations and high temperatures (> 26°C).