We have investigated the adsorption behavior of two organophosphorus pesticides Monocrotophos and Chloropyrifos onto Acid-Treated Palm Shell Powder (APSP) prepared from palm shells (agro-waste). The effects of adsorbent dose, contact time, and concentration on adsorption were studied. The Freundlich and Langmuir isotherms were applied to the experimental equilibrium data. Monolayer adsorption capacities Q(m) for spectrophotometric ((52.63 and 51.098) mg.g(-1) for Chloropyrifos and Monocrotophos, respectively) and for COD measurements ((14.25 and 11.57) mg.g(-1) for Chloropyrifos and Monocrotophos, respectively), have been evaluated. The calculated thermodynamic parameters Delta H, Delta S, and Delta G prove that Monocrotophos adsorption on APSP was feasible, spontaneous, and exothermic under the examined conditions, while Chloropyrifos did not show any appreciable change with temperature. The pseudo-first-order, pseudo-second-order, and intraparticle diffusion kinetic models were used to describe the kinetic data and evaluation of rate constants. The results of this study, with good correlation between spectrophotometric and COD measurements, imply the potential use of APSP as a low-cost adsorbent for removal of Chloropyrifos and Monocrotophos from industrial wastewater and runoff water from agricultural soils.