Activated carbon is a widely used industrial adsorbent mainly composed of carbonaceous material with relatively high surface area and porous structure. This attributes allows it to preferentially adsorb organic materials and other non-polar compounds from a gas or liquid stream resulting to its significant application in many industrial processes. This study investigates the adsorption efficiency of acidic treated activated carbon and its untreated activated carbon on the adsorption of lead (Pb) and 2,4-Dichlorophenol (2,4-DCP). The activated carbon was prepared from palm kernel shell as the precursor and was characterized based on its porosity having value of 0.18, iodine number of 440.95 mg/g, surface area of 433.65 m2/g and surface acidity value of 0.20 mmol H+/g. The palm kernel shell activated carbon was subjected to various treatment conditions of (40oC, 60oC, 80oC) temperatures, (30 minutes, 1 hour, 2 hours) treatment time and (1 M, 2 M, 3 M) concentrations of HNO3.The most suitable condition for the acidic treatment was determined by subjecting each of the treated activated carbon to surface acidity analysis. The highest surface acidity value of 2.55 mmol H+/g was obtained at treatment condition of 80oC, 2 hours and using 3 M concentration of the acid while the lowest value of 0.65 mmol H+/g was obtained at 40oC, 2 hours and 1 M concentration. Effect of the surface acidic treatment of the adsorbent on adsorption was investigated by comparing the adsorption capacity of the highly treated adsorbent with the untreated adsorbent for the adsorption of lead and 2,4-DCP. It was revealed that the treated adsorbent is better for the adsorption of lead while the untreated adsorbent is better for the adsorption of 2,4-DCP.