The objectives of this study are to find out the process of changes of the costume in the era of practical science, and to search the bukhak`s view of the costume. Conclusions are described as follows 1. The bukhak pursued the function and the rationality in men`s costumes, and dealed with the welfare point of view in the commons and humbles clothes, and criticized the phenomenon of over-fashion in women`s costume. 2. They contended for thrift against the luxury. But as they had also a modern thinking at the same time, they seemed to have a flexibility. Therefore they persued the essential courtesy in manners and costume. 3. The common people of Yi dynasty had the idea that yi dynasty is a small China replace by Ming dynasty. But the bukhak had a self-existent standpoint and a realistic idea to the Ch`ing dynasty. But they would have received the Mines culture as the reactionism in the costume. Chinese envied or ridiculed the korean costume. 4. It was the pursuit of the rationality that the Bukhak presented the direction of the costume. They contended for the growth of the business and the development of technique in order to reform the clothing industry.