An efficient ultrasound-assisted extraction (UAE) technique was applied to extract total phenolic content (TPC) from yarrow (Achillea beibrestinii). A response surface methodology was employed to evaluate the effects of 4 independent variables (temperature, pH, solvent to sample ratio, and time) on the TPC. The optimum extraction conditions were as follows: liquid to solid ratio 20, pH 6.3, extraction temperature $35^{circ}C$, and extraction time 35 min. Under the above-mentioned conditions, the experimental TPC was 11.7 mg gallic acid equivalent/g dry matter. $EC_{50}$ of the UAE extract at optimal conditions was found at $30.6{pm}0.6$ mg/L level and total flavonoids (TF) were obtained at $12.6{pm}0.2$ mg/10 g sample. Also, the results of HPLC analysis showed that gallic acid and p-coumaric acid were the predominant phenolic compounds in the plant.