<p>Ionophore antibiotics such as monensin, an anticoccidial drug widely used in veterinary medicine, are emerging contaminants frequently present in aquatic and terrestrial ecosystems, posing a noteworthy challenge for the environment and human health due to their high toxicity. One of the strategies to deal with this problem could be the use of cheap, non-toxic and available biomaterials that could act as bio-adsorbents. In this study, batch-type experiments were used to characterize monensin retention onto six different agro-food by-products from Tunisia (specifically orange and pomegranate peels, pea and almond shells, date palm stones, and coffee grounds) at monensin concentrations of 5, 10, 20, 40, 80 and 100 µmol L^-1. All determinations were performed employing HPLC-UV equipment. The adsorption rates were generally higher than 65% when low monensin concentrations were added, while decreased for doses above 20 µmol L^-1, especially for pomegranate peel and coffee grounds. Overall, almond shell and orange peel performed better, exceeding 91.9% adsorption in all cases. Adsorption data fitted well the Freundlich and Temkin models for all samples, except for pomegranate peel and coffee grounds, which showed better adjustment to the Langmuir model. Regarding desorption, it was generally low, not surpassing 18.2% (coffee grounds at 100 µmol L^-1 of monensin) in any case. These findings have relevant implications for addressing monensin contamination in environmental compartments, offering insights into the use of agro-food wastes as valuable and efficient biomaterials for this anticoccidial.</p>