Petasites japonicus (PJ) has been used traditionally as the treatment or the prophylaxis of migraine and tension headache in Asia. In the present study, to we compared the characteristics of PJ powder and extracts obtained by various methods utilize the PJ as a functional material. PJ powder by freeze-drying possessed 6.61% water content, 4.51% crude fat, 23.75% crude protein, 18.62% crude ash, 46.97% carbohydrates, and crude fiber 39.22%. It contained a particularly high potassium content in mineral. Among different extraction methods, extracts of 50% (PJ-50E) or 70% ethanol (PJ-70E) showed the highest total polyphenol content and antioxidant activity, while cold-water extraction (PJ-WE) showed the lowest. However, when the α-glucosidase inhibitory were analyzed, PJ-WE was highest while the treatment extracted ethanol were not active at all. In anti-inflammatory activity by RAW 264.7 and HaCaT cells, PJ-WE showed significantly higher inhibitory activity in comparison to those of the other extract. In conclusion, it is considered that the water-extraction method is better than other extraction methods for practical preparation of functional materials with high α-glucosidase inhibitory and anti-inflammatory activities from PJ.