Response surface methodology (RSM) was applied to predict optimum conditions for microwave-assisted extraction (MAE) of flavonoid from Radix Astragali. A central composite design was used to monitor the effect of temperature, extraction time, solvent-to-material ratio, and the ethanol concentration on yield of total flavanoid (TFA). Optimum extraction conditions were predicted as 108.2 degrees C, 26.7 min, 23.1 ml/g solvent-to-material ratio and 86.2% ethanol. The maximum yield 1.234 +/- 0.031 mg/g was close to the yield of Soxhlet and higher than that of ultrasound assisted extraction and heat reflux extraction. MAE was an effective alternative to conventional extraction methods.