Two field experiments were carried out at Shandaweel Agric. Res. Station, Sohag, Egypt during 2004 and 2005 seasons, to evaluate the susceptibility of seven genotypes of maize and sorghum to infestation by the corn leaf aphid, Rhopalosiphum maidis (Fitch) and the greenbug, Schizaphis graminum (Rondani.). The genotypes of maize were 10, 122, 123, 124, 129, 155 and Watania 4, whereas for sorghum Dorado, Kymone, R-89039, R-91022 were short genotypes, while Giza 15, Giza113, and R-2735 were long ones. The obtained results revealed that: 1) In case of maize genotypes, the numbers of R. maidis, which is a major pest on the seven maize genotypes were significantly lower in the first season than in the second one. Single cross 10 was the most susceptible genotype to infestation by this aphid, whereas single cross 155 was the least susceptible ones, during 2004 and 2005 seasons. The tested genotypes were grouped into: moderate resistant (single cross 155 during 2004 and 2005 seasons and Watania 4 during 2005 season), Low resistant (Watania 4 in 2004 season, single cross 123 during 2004 and 2005 seasons and single cross 124 in 2005 season) and susceptible (genotypes 124 in 2004 season and 129, 122 and 10 during 2004 and 2005 seasons. 2) In case of sorghum genotypes: in regard to R. maidis, Dorado was more susceptible to aphid infestation than the other genotypes, while kymone was the least susceptible ones. The tested genotypes were grouped into: moderate resistant (Kymone in 2005 season) Low resistant Kymone in 2004 season and Giza 113, R-91022, R-89039 during 2004 and 2005 seasons, susceptible (Giza 15, R-2735 and Dorado during both seasons. Concerning S. graminum, Giza 15 harbored the highest numbers of aphids, while Kymone attracted the least ones during both seasons. The tested genotypes were grouped into moderate resistant (Kymon in 2005 season), Low resistant (Kymon in 2004 season and Dorada, Giza 113 and R-89093 during both seasons) and susceptible (R-91022, R-2735 and Giza 15).