Porous carbons (PCs) were prepared from seawater (SW)-impregnated sawdust (SD) by CO 2 activation at 700 °C. The preparation process was investigated on-line by thermogravimetric analyzer coupled with FTIR (TG-FTIR). PCs were characterized by N 2-adsorption/desorption and Fourier transform infrared spectroscopy. The adsorption abilities of PCs for oxytetracycline (OTC) were compared and the adsorption isotherms of OTC on the optimum sample were studied. Results showed that SW impregnation led to the release of more CO from SD at 700 °C, indicating a higher degree of CO 2 activation, thus a 81% higher BET surface area (S BET) can be achieved under the same activation condition. Mesopore volume of PC increased from 0.089 to 0.301 cm 3 g −1 with the activation time increasing from 5 to 60 min. PC obtained after 60-min activation with a S BET of 490 m 2 g −1 and an average pore diameter of 3.78 nm had the highest adsorption ability for OTC. Its adsorption equilibrium data for OTC followed Langmuir model with a maximum monolayer adsorption capacity up to 100 mg g −1 .