There are compelling economic and environmental reasons to remove pesticides from wastewater because they are toxic and carcinogenic. The effectiveness of copper-based metal–organic framework (Cu-BTC) for adsorbing the insecticide 14C-ethion from wastewater has been studied as function of contact time, adsorbent dosage, temperature and pH. 14C-ethion/Cu-BTC isotherms exhibit two plateaus (BET type IV) and are reliably represented by Brunauer–Deming–Deming–Teller and Zhu–Gu models, with deviations of only 1.99 and 3.95%, respectively. The removal curve measured under batch operation is well represented by a pseudo-first-order equation, yielding results equivalent to the theoretical linear driving force model of Glueckauf. At pH 7, 75 mg L−1 ethion concentration, 150 min, 25 °C and 0.425 g L−1 Cu-BTC dose, the sorbent capacity is ca. 122 mg g−1. Moreover, Cu-BTC has a good stability after six adsorptions cycles. Finally, our results disclose the fundamental understanding of the adsorption mechanism: the ethion molecule coordinates to two copper(II) atoms across the metal–organic framework channel via the phosphoryl (P–O) group.