Field experiments were conduced at El-Giza Research Station dur­ing the two successive seasons (1995/1997)to determine the effect of sowing date of barley on its infestation with the corn leaf aphid, Ropalos­iphum maides. (Fitch) (Homoptera: Aphididae) and yield components. Testing sowing dates were 23/11, 8/12 and 23/12 in the first season and 26/11, 11/12 and 26/12 in the second one. For both seasons of investigation, aphids colonized barley plants in the early stages of their life in negligible number. The mean total numbers of aphids/tiller in 1995/96 was comparatively low for the three sowing dates(5.52,4.64 and 2.75, respectively) comparted to that for 1996/97 (40.71,23.46 and 13.68, respectively). Peaks of infestation occurred at mean weath­er conditions of 10-11°C and 63-73% R.H.Both biological and grain yield were affected under heavy aphid infestation. The first sowing date showed the highest significant values of biological and straw yield com­pared to the other two tested sowing dates. The highest grain yield was took place at the second sowing date.