Objective To study on the effects of different factors on the extraction of total flavonoids from leaves of Psidium guajava and optimize the ultrasound assisted extraction of total flavonoids by using response surface methodology. Methods Ethanol concentration,ratio of material to liquid and ultrasonic power were evaluated basing on single factor experiments with the yields of total flavonoids as index. Then response surface methodology with three-factors and three-levels was carried out for optimizing the ...