This research focuses on functionalism in American fashion designs which have become the center of public attention in recent. First, documentary studies about how functionalism, which originated in Europe in the beginning of the 20th century, has been developed throughout the 20th century were preceded Second, content analysis was done for the articles, including the word ‘unction’,‘utility’ and ‘practical’in the New York Times and American Vogue from January 1990 to January 2001. As a result, functionalism in 1990s has been developed in different ways from the mechanical, organic, and mea analogies of functionalism in the beginning of 20th century. It doesn't belong to an analogy but has the fused characteristics of those three analogies. It can be classified into techno functionalism influenced by new technology, pure functionalism related to minimalism, sports casual functionalism for those who are crazy about the speed and sports and enjoy the freedom and comfort, and symbolic functionalism which stresses Zen style. More casual manners of formal wear are distinct elements in functionalist fashion design in 1990s. It leads to strong expressions of sports casual functionalism, which plays a great role in sportswear industry of American fashion design. The American fashion designers who were mentioned often in the articles were Donna Karan, Calvin Klein, Ralph lauren and Tommy Hilfiger. As well as their works have common formative features based on functionalism, each of them shows his/her own strung color. A]1 of these designers make American fashion design, which can be defined as casual wear or sportswear, very popular worldwide based on the developed American functionalism. Functionalism considering practical and conceptional functions will continue in coming century and techno functionalism and sports casual functionalism in future fashion designs wilt be expressed more strongly with new technology and casual trends of life style.