During a two-year (2004-2005) survey of alfalfa aphids and their natural enemies in Isfahan, a total of four aphid species and 58 species of their natural enemies comprised of 45 predatory species, 11 parasitoid species and two species of parasitic mites were collected and identified. Moreover, five hyperparasitoid species were collected. On each sampling date, six 20-sweep samples were taken using a 38cm-diameter sweep-net and also six 20-stem were sampled. The results showed that the mean percent of Hippodamia variegata Goeze, Nabis spp., Deraeocoris spp., Orius spp., Geocoris spp. and aphid parasitoids in strip-harvested field were 38%, 95%, 119%, 57%, 100% and 122%, respectively; higher than those in conventionally-harvested field. In contrast, the mean percent of Acyrthosiphon pisum (Harris) and THERIOAPHIS trifolii (Monell) forma MACULATA (Buckton) were 24% and 28%, respectively; lower in strip-harvested field than in conventionally-harvested field.