This study aims to determine the insecticidal effect of Mentha rotundifolia essential oil on the post-harvest cereal pest Rhyzoperthadominica and to evaluate the doses and times required to kill 50% and 90% of the insect populations through two tests: contact and inhalation. The results show a strong biocidal effect on adult of Rhyzoperthadominica due to the different doses applied over time. The lethal dose DL50 was estimated to kill 50% of the insects with 0.377 µL in the contact test, while the lethal doses DL50 and DL90 were estimated to kill 50% and 90% of the insect population with 1.187 µL and 4.390 µL in the inhalation test. The essential oil of Mentha rotundifolia is toxic and can thus be used as a biopesticide.