Excessive nitrate discharge into aquatic environment is a serious concern as it gives huge impacts on aquatic life as well as corrupts ecosystem and water sources. The effective treatment of nitrate-containing wastewater is essential for the sake of health and environmental protection. In this study, the adsorption of nitrate was carried out using porous rice husk silica functionalized with branched polyethyleneimine (RSi-bPEI). A series of experiments were conducted to measure several adsorption conditions, adsorption isotherms, kinetics, selectivity and reusability. Experimental results demonstrated that the functionalization with branched PEI (bPEI) has significantly improved the adsorption about 40 higher. The ideal conditions for the nitrate adsorption onto RSi-bPEI is at pH = 4, 0.5 g L-1 dose, 50 mg L-1 concentration and about 120 min adsorption time. The pseudo-second-order and Langmuir equations were the most suitable models to describe the nitrate sorption from aqueous solution with high correlation coefficient (0.99). The monolayer adsorption capacity was found to be 94.49 mg g-1 for RSi-bPEI and 47.46 mg g-1 for RSi. The reusability test manifested RSi-bPEI has good regeneration capacity, hence can be an ideal adsorbent for practical wastewater treatment. © 2019 Published by Elsevier Ltd.