The purpose of this study was to establish a sizing system according to size and dimension whereby manufactured pants can be classified and develop men’s formal pants pattern based on the analysis of ready-made and educational pants pattern. The first, we surveyed the sizing and the basic pants patterns of the men’s ready-made wear companies, Secondly, through the survey data of the domestic men’ready-mad clothing industry, we proposed a new sizing system. Lastly, after compared three different types of ready-mad pants manufactured according to their patterns and an additional type of pants made after the educational pattern, the new men’s basic pants pattern were developed. The findings were as follows: 1. Survey of the domestic ready-mad garment industry showed that each company classified its own manufactured goods according to its own sizing system: moreover, they each used its own unique patterns which appeared to be resulted from a combination of two factors : the experience of a patterner and foreign know-how technology. 2. New sizing system was developed with 12 steps from size 74-88 to size 96-106 based on the high frequencies of the companies’3. New basic patterns for men’s formal pants were developed: Inseam length = 80cm, crotch line = H/4+4.6cm, pants ham = 23.5cm as basic lines and front waist girth =W/4+9.1cm as drafting line. 4. the superiority of the new basic patterns were been demonstrated by a high approval rate of the subjects who participated in testing.