Adsorption characteristics of the pesticides Deltamethrin and Lambda-Cyhalothrin were studied in aqueous solutions using oil shale ash (OSA) as an adsorbent. The maximum loading capacity of the adsorbent and the rate of adsorption were found to increase with increasing the pesticides initial concentration, mixing speed and decreases with temperature, particle size and pH. Langmuir as well as Freundlich isotherm models fit the adsorption data with R-2 > 0.97 in all cases. When the initial concentration was 15 mg/l, Q(max) values obtained with OSA having 202.25 mu m average diameters, 25 degrees C, 400 rpm mixing speed and pH 3 were 11.4 and 8.6 mg/g, respectively. The desorption experiments using acetate buffer showed a maximum recovery of 74% for Deltamethrin and 45% for Lambda-Cyhalothrin.