<p>Dimetridazole is a well-known antibiotic with broad-spectrum activity. However, it has been found in water environments, emphasising the significance of detecting antibiotics in aquatic settings. In this study, exfoliated MoSe₂ nanosheets were combined with electrochemically reduced graphene oxide to develop a simple, efficient sensor for the electrochemical detection of dimetridazole in aqueous samples. The graphene oxide was synthesised using the modified Hummers method, dispersed in acidified Na₂SO₄, and then electrodeposited onto a glassy carbon electrode decorated with exfoliated MoSe₂ sheets to produce GCE/MoSe₂/rGO. The optimal detection of dimetridazole was observed at pH 7.0. Linear calibration curves were obtained for concentrations ranging from 10 nM to 260 µM, with a sensitivity of 2.60 µA µm^− 1 cm^− 2 and a detection limit of 4.0 nM. Excellent stability was observed, with no detectable loss in the peak current over a week in the continuous presence of dimetridazole. Very good selectivity was achieved against inorganic anions commonly present in aquatic environments. When real water samples were spiked with dimetridazole, recoveries ranged from 90.5% to 105.8%.</p> Graphical Abstract