Functional compound extracted from Petasites japonicus leaves has been known to be effective in the allergic asthma treatment. In this study was carried out to optimize the extraction process of functional compound from Petasites japnicus leaves by response surface methodology. Independent variables were ethanol concentration (40~80%), extraction rpm (125~225), and extraction time (1~3 hr) by box-behnken design, and extraction yield, petasin content, total polyphenolics and DPPH (radical scavenging activity) were considered as the dependent variables. The extraction yield was getting higher in proportion to ethanol concentration, extraction rpm, and extraction time the was concluded in ethanol concentration of 65.02%, extraction rpm 223.37, extraction time 2.03 hr maximum value at 39.50%. In a case measuring petasin content had a great relation with not extraction rpm or extraction time but ethanol concentration, and the was concluded in ethanol concentration of 79.92%, rpm 178.10, the extraction time is 2.06 hr maximum value of 659.29 μg/g. Total polyphenolics was high in these situations that both ethanol concentration and extraction rpm are entirely lowest or highest, and the of total polyphenolics ethanol concentration of 55.21% for the sample, extract rpm 129.71, extraction time 1.65 hr maximum value of 47.67 mg/g. In a case of DPPH radical scavenging activity showed high activity in relation with ethanol concentration and extraction time getting higher, and the of ethanol concentration of 69.80% for the sample, extract rpm 178.11, extraction time 2.87 hr maximum value was 85.49%. Of optimum extraction conditions petasin ethanol the petasin content, sexuality impact as a result of the above, the ethanol extract of Petasites japonicus leaves extract yield of conditions has been confirmed concentration of 79.91%, extraction 178.10 rpm and 2.06 hr were determined.