Experimental and theoretical studies have been conducted to investigate the adsorption of atrazine in aqueous solutions by sheep manure-derived biochar synthesized at 650°C (SMB650). The results of characterization analysis showed that SMB650 possessed large specific surface area and was rich in pore structure and functional groups. The removal efficiency of atrazine by SMB650 was 95.3% under the optimum conditions, of which contact time, initial atrzaine concentration, initial solution pH, SMB650 dosage and temperature were 150 min, 1500 μg/L, 3.0, 1.6 g/L and 25ºC, respectively. The results of kinetic and isotherm studies revealed that the pseudo second-order and the Freundlich model fit the experimental data best (R²>0.98). The adsorption of atrazine onto SMB650 belonged to multi-molecular layer adsorption. The calculated thermodynamic parameters like free energy change (ΔG^θ), enthalpy change (ΔH^θ) and entropy change (ΔS^θ) were -7.8730 to -6.2976 kJ/mol, 17.2179 kJ/mol and 0.0788 kJ/(mol·K), respectively, indicating that the adsorption process of atrazine onto SMB650 was spontaneous, endothermic and entropy-increased. The present study showed that the sheep manure-derived biochar could be used as a promising adsorbent for the removal of atrazine from aqueous solutions.