This work includes the synthesis of ten heterocyclic compounds (3a-i and 4) containing pyrimidine moiety incorporated in their structures. Structure characterizations of these compounds were performed by using elemental and spectroscopic analyses. Their toxicity as potential insecticidal agents against the adults and nymphs of cowpea Aphid, Aphis craccivora Koch was evaluated. The results of this toxicological activity test revealed that a reasonable number of these compounds possess excellent toxicological activity against cowpea aphids such as compounds (3d), (3c), and (3b) with LC50 values 0.0125, 0.0134, and 0.0383 ppm, respectively. The toxicological activities of the rest of the tested compounds ranged from good to moderate against the same insects.