This study was devoted to the valorization of a plant waste (olive stones): that is widely available in Mediterranean countries in order to remove mercury from natural gas. The raw material from olive stones was prepared by pyrolysis, chemical activation with phosphoric acid, and physical activation under steam. Two olive stone-based granular activated carbons were prepared: one with the virgin stones, while the other was impregnated with sulphur. After treatment, the adsorbents obtained were characterized by determining the iodine number, the methylene blue index, and by estimating the porous properties by N-2 adsorption at 77K. Thermogravimetric analysis and infrared spectroscopy analysis were carried out to determine the functional groups before and after mercury adsorption. An experimental study of vapour-phase mercury adsorption by the activated carbons (virgin and sulphur-impregnated) and a comparison with a commercial material (HGR) were performed. The comparison, made by analyzing the adsorption in a continuous mode, showed that the proportion of sulphur and the porosity were important for the removal of mercury. In the conditions used, the mercury adsorption on the ACs studied follows a physisorption mechanism. The results showed that granular activated carbon-based olive stones (sulphur-impregnated) are very efficient to remove mercury (with 2864g/g) and also less expensive than commercial activated carbon due to their local availability.