Oil palm shell as a raw material was used for the preparation of activated carbon adsorbents. The precursor was first activated chemically with small proportion of zinc chloride and phosporic acid and then the prepared samples were treated with CO2 flow at 850°C at different activation time. The samples activated chemically with phosphoric acid showed higher surface area and pore volume compared to the samples activated using zinc chloride as chemical agent, at the same duration. In addition, it was shown that extra physical activation will grantees more developed pore structure. In terms of pore size distribution the combined preparation method resulted in a better and more homogenous pore size distribution than the commercial palm shell based activated carbon.