Aluminum (Al) was impregnated onto lignocellulosic materials (Juniperus monosperma) to develop inorganic/organic hybrid adsorbents for removing orthophosphate from water. Surface modification of the bio-renewable materials by impregnation of an inorganic moiety extended the applicability from heavy metal removal to anion removal in water. Al components were loaded onto juniper wood, an organic substrate, under three different pH conditions (pH 3.0, 3.7, and 4.7) resulting in three Al-impregnated adsorbents, named Al/JW01, Al/JW02, and Al/JW03, respectively. Adsorption kinetic experiments, performed with a pH of 5.0 ± 0.1 and an initial phosphorus, P, concentration of 10 ppm, demonstrated orthophosphate adsorption capacities of up to 0.0456 mmol P/g, which were nearly proportional to the Al loading amounts. The adsorption capacities of Al/JW02 and Al/JW03 acquired from the adsorption isotherm were 0.0943 and 0.132 mmol P/g, respectively, which are comparable to those of other inorganic adsorbents. The adsorption densities (0.302 mmol P/mmol Al for Al/JW02 and 0.291 mmol P/mmol Al for Al/JW03) suggest that the reaction between orthophosphate and Al was inner-sphere binding. The decrease in P uptake below pH 4 observed in the adsorption envelope was caused by the release of loaded Al from the adsorbents.