Developing an eco-friendly, sustainable and antibacterial adsorbent is significant for actual water treatment. Herein, a bio-based antibacterial adsorbent based on titanium dioxide (TiO2) nanoparticles functionalized chitosan (CS) was prepared through an in-situ hydrolysis strategy using titanium oxysulfate as the source of TiO2. The as-obtained CS/TiO2 nanocomposite was characterized by a variety of analytical techniques. According to the Langmuir mode, the adsorption capacity of CS/TiO₂ reached 23.64 mg P g^{− 1}, almost 8 times higher than that of CS. In addition, the normalized adsorption capacity (adsorption value per Ti) of CS/TiO₂ was calculated to be 102.68 mg P g^{− 1} Ti^{− 1}, much higher than pure TiO2 (60.11 mg P g^{− 1} Ti^{− 1}). Moreover, CS/TiO2 exhibited a highly selective capacity for phosphate removal in the presence of competing anions, and showed high stability in a wide pH range of 3.0–8.0. When the phosphate concentration was 2.0 mg P L^{− 1}, the removal efficiency of phosphate reached 99.5 % and the residual concentration was only 10 μg P L^{− 1}, which meets the USEPA standards for eutrophication prevention and control. In addition, after treatment by CS/TiO₂, the phosphate concentration of two sewage water samples decreased from 1.50 and 1.0 mg P L^{− 1} to <0.10 mg P L^{− 1}, meeting the standard of level II water based on the Environmental Quality Standard of China (GB3838–2002). Ligand exchange and electrostatic interactions are mainly responsible for phosphate adsorption by CS/TiO₂. Furthermore, the CS/TiO₂ nanocomposites exhibited excellent antibacterial activity, which could avoid biofouling contamination caused by microorganisms. Benefiting from the above advantages, the as-designed CS/TiO² nanocomposite has great potential as a bio-based antibacterial adsorbent for phosphate capture or removal from wastewater.