Alum sludge refers to the by-product from the processing of drinking water in Water Treatment Works. In this study, groups of batch experiments were designed to identify the characteristics of dewatered alum sludge for phosphorus adsorption. Air-dried alum sludge (moisture content 10.2%), which was collected from a Water Treatment Works in Dublin, was subjected for artificial P-rich wastewater adsorption tests using KH 2 PO 4 as a model P source. Adsorption behaviours were investigated as a function of amount and particle size of alum sludge; pH of solution; and adsorption time. The results have shown that pH plays a major role not only in the adsorption process but also in the adsorption capacity. With regard to adsorption capacity, this study reveals the Langmuir adsorption isotherm being the best fit with experimental data (R 2 =0.98-0.99). The maximum adsorption capacities range from 0.7 to 3.5mg-P/g when the pH of the synthetic P solution was varied from 9.0 to 4.3, accordingly. The outcome of this study indicated that alum sludge is suitable for use as an adsorbent for removal of phosphate from wastewater.