Background. The aim of this study was to determine the best extraction conditions for total phenolic content (TPC) and antioxidant capacity (AC) of Polygonum multifl orum Thunb. root using microwave-assisted extraction (MAE). Material and methods. The raw material used was Polygonum multifl orum Thunb. root powder. Five factors such as solvent type, solvent concentrations, solvent/material ratio, extraction time and microwave power were studied; TPC and AC values were determined by the Folin-Ciocalteu method and DPPH free radical scavenging activity measurement, respectively. In addition, studies involved assaying the HPLC test of extracts and SEM of samples. Results. Optimal results pointed to acetone as the solvent, acetone concentration of 60%, solvent/material ratio of 40/1 (v/w), extraction time of 5 mins and microwave power of 127 W. TPC and AC obtained were approximates 44.3 ±0.13 mg GAE/g DW and 341.26 ±1.54 μmol TE/g DW, respectively. The eff ect of microwaving on the cell destruction of Polygonum multifl orum Thunb. root was observed by scanning electron microscopy (SEM). Some phenolic compounds were determined by the HPLC method, for instance, gallic acid, catechin and resveratrol. Conclusion. These factors signifi cantly aff ected TPC and AC. We can use acetone as a solvent with microwave-assisted extraction to achieve the best result.