An artificial hair and a wig using the same are provided which have the property of thermal deformation expanding upon heating by a hair drier or others used for hair styling.The artificial hair 1 is made by mixing at the pre-determined ratio a semi-aromatic polyamide having a glass transition temperature between 60-120° C. and a resin not expanding in said temperature range. The artificial hair may have a sheath/core structure comprising a core portion 5B and a sheath portion covering the core portion. As the resin not expanding in said temperature range, polyethylene terephthalate or others can be used, and as the sheath, nylon 6 or nylon 66 can be used. Said artificial hair 1 can maintain its shape at room temperature or after shampooing due to thermal deformation by heating in steam atmosphere at temperature of glass transition or higher or about 80-100° C.