A novel bio-adsorbent (DACS-TA) was synthesized via a facile crosslinking reaction between tannin acid (TA) and dialdehyde corn starch (DACS), and the adsorption behavior of Au(III) from aqueous solution onto the DACS-TA was evaluated in batch adsorption experiments. Fourier Transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectroscopies were used to verify the successful crosslinking reaction, and the surface functional groups and the thermal stability of the prepared DACS-TA were also characterized. Adsorption results showed that the DACS-TA exhibited high adsorption capacity and selectivity towards Au(III), and the maximum adsorption capacity could reach up to 298.5 mg/g at pH 2.0 according to the Langmuir fitting. The adsorption isotherms of Au(III) on the DACS-TA were described well by the Langmuir model, indicating that the monolayer adsorption of Au(III) possibly occurred on the adsorbent surfaces. The kinetic data were fitted better by the Pseudo-second-order kinetic equation in comparison with the Pseudo-first-order and Intraparticle diffusion equations. Based on the SEM, XRD and XPS analysis, the adsorption-reduction mechanism of Au(III) on the DACS-TA was proposed. Namely, Au(III) was first adsorbed on the adsorbent and then was reduced to Au(0) while the phenolic group of TA was oxidized to carbonyl groups.