•Alfalfa and bermudagrass-derived biochars were used for removal of tetracycline.•Based on the physicochemical properties, adsorption mechanisms were explained.•The alfalfa-derived biochar has exhibited outstanding TC adsorption capacity.•Adsorption capacity of alfalfa-derived biochar was compared to commercial ACs.•Alkaline regeneration led to effective adsorption–desorption for multiple cycles. The biochars derived from alfalfa (AF) and bermudagrass (BG), the abundant grass hays to cows, were prepared, characterized and used for removal of tetracycline (TC) in water. The alfalfa-derived biochar (AF-BC) has exhibited outstanding TC adsorption capacity (372 mg/g), which was about 8-fold higher than that of bermudagrass-derived biochar (BG-BC). In addition, the TC adsorption capacity of AF-BC was comparable with those of the commercial activated carbons under the same conditions. The surface structure, chemistry and high ash contents of AF-BC suggested the hydrogen bonding, electrostatic interactions and surface complexation between AF-BC and TC. Furthermore, hydroxyapatite (HAP; Ca5(PO4)3OH) and calcite (CaCO3) on the surface of AF-BC may also contribute to adsorption of TC via surface complexation, hydrogen bonding and electrostatic interactions. The alkaline desorption-driven regeneration of TC-spent AF-BC led to effective adsorption–desorption for multiple cycles, which indicated AF-BC could be a cost-effective adsorbent for TC in water and wastewater.