This study aimed to test the teratogenic and antiteratogenic potentials of Cosmos sulphureus leaf and petal extracts, by employing the Dominant Lethal Test in white mice. Specifically, it determined the following: l) if there are observable teratogenic and antiteratogenic potentials of the Cosmos sulphureus leaf and petal extracts as compared to the controls in terms of the fertility index, gestation index, implantation index, percent dead implants and mean fetal weight; and 2) if there are any significant differences on the teratogenic and antiteratogenic potentials among the different treatments in terms of the fertility index, gestation index, implantation index, percent dead implants and mean fetal weight. Male mice were treated with the treatments for seven days. Then, six days after the last treatment was given, they were mated with the virgin female mice on a 1 male:2 female ratio. Findings revealed that: 1)tetracycline exhibited genotoxicity to male germ cells, hence teratogenic. It induced reduction of fertility index, gestation index, implantation index and higher percent dead implants. It had also the lowest mean fetal weight. It is possible that this genotoxin or mutagen altered the DNA structure of the sperm cells' DNA by interacting with the DNA base pairs through intercalation stabilized by hydrogen bond causing chromosomal damage; 2) Cosmos sulphureus Cav. leaf and petal extracts did not exhibit genotoxicity to male germ cells, hence non-teratogenic. The extracts induced a higher fertility index, genstation index, implantation index and mean fetal weight, and lower percent dead implants when compared to the positive control.This could be explained by the presence of rich flavonoids which have a strongg antioxidant potential. Based on the findings of the study, the following are concluded: 1) There are observable teratogenic and antiteratgenic potentials of the Cosmos sulphureus Cav. leaf and petal extracts as compared to the controls in terms of the folowing parameters: fertility index, gestation index, implantation index, percent dead implants, and mean fetal weigth; and 2) There are no significant differences on the teratogenic and antiteratogeni potentials between the different treatments in terms of the fertility index, gestation index, implantation index and percent dead implants, except for mean fetal weight. However, the extracts have higher fertility, gestation and implantation indices and mean fetal weight, while lower percent dead implants compared to tetracyline. It is recommended that other parts of the plant may be screened using Dominant Lethal Test.