Nitrogen-doped carbons (NDCs) as CO2 adsorbents have triggered immense research interest. The preparation of NDCs using different methods has been widely investigated. In this work, a novel synthesis strategy for NDCs was proposed, where zinc nitrate played the roles of an activation agent and a nitrogen source at the same time. The naturally abundant agar was used as the carbon source. Agar was first carbonized at 500 degrees C, and the obtained carbon was then activated with zinc nitrate at different temperatures. The experimental results showed that zinc nitrate activation significantly improved the carbon's surface area. Excessive zinc nitrate caused the enlargement of pores and the decrease of surface area. The effects of the addition amount of zinc nitrate and the activation temperature on the physicochemical properties of the NDCs were studied and discussed. The NDCs were also investigated for CO2 adsorption. At low pressure, the adsorption was correlated with small micropores. Moreover, pore enlargement and the loss of doped nitrogen had negative effects on adsorption heat and selectivity. For adsorption at high pressure, the carbon activated at 950 degrees C showed a high CO(2 )uptake of 15.7 mmol/g at 0 degrees C and 20 bar. A linear relationship was observed between the uptake at 20 bar and the specific surface area of the carbon, while nitrogen doping did not show any obvious influences on the adsorption.