Reflecting the consumer’s desire to look young, the “down-aging” trend, which blurs the distinctions between age groups, is the latest craze in the fashion market. The popularity of this trend made brand identities similar, resulting in customers becoming more interested in segmented notions of fashion (in terms of the story, design, high-quality material, etc.) regarding the product, and in particular, focus has become oriented to the fitness to the human body. In this sense, the researcher aimed to develop the prototype of a slim-fit tailored jacket that fits the standard somatotypes of women in their 30s well. For the purpose of this research, slim-fit tailored jackets from existing brands were collected and analyzed, and a subsequent wearability test was conducted based on the standard somatotype of women in their 30s. The research patterns were prototype of the developed slim fit tailored jacket are bust size of 3.8 cm, waist of 7 cm, and hip size of 3.8 cm. Then the research patterns were selected to develop the prototype of a properly fitting slim-fit tailored jacket. As outlined above, the development of a slim-fit tailored jacket prototype for the standard somatotypes of women in their 30s was conducted by solving the fitness issues of existing brands in order to produce properly fitting jackets that satisfy consumers.