Herein we present a facile approach for the preparation of a novel hierarchically porous carbon, in which seaweeds serve as carbon source and KOH as activator. The fabricated KOH-activated seaweed carbon (K-SC) displays strong affinity towards tetracycline (TC) with maximum uptake quantity of 853.3 mg g–1, significantly higher than other TC adsorbents. The superior adsorption capacity ascribes to large specific surface area (2614 m2 g−1) and hierarchically porous structure of K-SC, along with strong π–π interactions between TC and K-SC. In addition, the as-prepared K-SC exhibits fast adsorption kinetics, capable of removing 99% of TC in 30 min. Meanwhile, the exhausted K-SC can be regenerated for four cycling adsorption without an obvious degradation in capacities. More importantly, pH and ionic strengths barely affect the adsorption performance of K-SC, implying electrostatic interactions hardly play any role in TC adsorption process. Furthermore, the K-SC packed fixed-bed column (0.1 g of adsorbents) can continually treat 2780 mL solution spiked with 5.0 mg g–1 TC before reaching the breakthrough point. All in all, the fabricated K-SC equips with high adsorption capacity, fast adsorption rate, glorious anti-interference capability and good reusability, which make it holding great feasibilities for treating TC contamination in real applications.