Abstract: Biochars were prepared from rice husk and chicken manure, and then were modified with HNO₃ and NaOH. The effect and mechanism of modified biochar on adsorption of naphthalene were studied. XRD, specific surface area analysis, and infrared spectroscopy were used to characterize the biochar, and the effects of parameters such as adsorbent dosage, solution pH value, and modifying conditions on the adsorption were investigated. The results show that the average pore diameter of the modified biochar decreased, and the total pore volume and the specific surface area increased except for HNO₃ modified rice husk biochar. The oxygen-containing functional groups of biochar modified with HNO₃ increased, and the aroma of rice husk biochar modified with NaOH increased. The adsorption isotherms of naphthalene by biochar were better fitted by Freundlich model, and NaOH modified rice husk biochar had the best adsorption effect. As adsorbent dosage increased, the unit adsorption capacity of naphthalene decreased; as the pH value of the solution increased, the adsorption capacity of naphthalene by biochar decreased. The modifying conditions show that rice husk biochar is more suitable for NaOH modification; and chicken manure biochar is more suitable for HNO₃ modification, and the higher the HNO₃ concentration, the better the adsorption effect. The adsorption mechanism of naphthalene by biochar might be void adsorption, especially microporous adsorption, and there was also a part of π-π interaction.