The problem of water pollution with pesticides is one of the most dangerous types of pollution, as it is considered one of the most important causes of cancer for humans, as well as the destruction of the aquatic environment. Currently, several techniques have been used to solve this problem, the most prominent of which is the adsorption technique. The purpose of this study is to investigate the removal of hymexazol pesticide from an aqueous solution by using a cadmium oxide nanopartical adsorbent. CdO NPs were prepared by the photolysis method, and they were characterized by several characterization techniques, such as XRD, TEM, and FE-SEM. Batch adsorption experiments were performed using a variety of factors, such as contact time, adsorbent dose, initial pesticide concentration, and temperature. The results showed that the removal efficiency of hymexazol pesticide on CdO NPs was the highest at a contact time of 50 minutes. The equilibrium data were well fitted with Freundlich mode. The kinetic investigations reveal that the pseudo-second-order model can describe hymexazol pesticide adsorption processes. According to the thermodynamic study, hymexazol pesticide adsorption is a physisorption-endothermic and spontaneous process.