Abstract: The present studies were carried out throughout the period from 2008-2009 and 2009-2010. The main objectives were to study population age structure of the cabbage aphid infesting canola (Brassica napus) in Assiut, Upper Egypt and their natural enemies. Data show that the migration of aphids from their overwintering sites into canola fields occurred after about 23 days (during the third week of December). The population then increased to become 10% of the maximum number after 49 days (during the third week of January). Maximum population densityof the cabbage aphid occurred after about 97 days. Therefore, the peak of abundance could be expected around the end of February – beginning of March. After the population reached its highest level it declined and reached 10% of the maximum after 112 days. The population then vanished from the field after 122 days (toward the end of March). The present results indicate that the number of cabbage aphids was significantly higher in the first season 2008-2009 (938.79 aphids/plant), than that of 2009-2010 season (244.77 aphids/plant). The differences in levels of infestation between the seasons might be attributed to the differences in weather factors (temperature, relative humidity) and/or the effect of the common natural enemies in each season.