The origin and structural development of Do-po have been studied with a consideration of the back piece of Do-po in this paper. This study found that Do-po was in this paper. This study found that Do-po was originally imported from China. This paper reports that an earlier record on Do-po is found in an epitaph(1564) than the record found in S njoSilnok(1607) which is conventionally known as the earliest record on Do-po. The structure of Do-po has been widely known as an“attachment of J n-sam”on slitted back piece of the outwear. However, this study shows that Do-po has been formed by inserting the gusset of the front piece into the back piece of the outwear Jik-nyung. This change can be considered as the economical and practical needs to save the cloth or by the aethetical need of simpler clothing. This study also classifies the shape of gussets largely into nine classes according to the temporal development in the shape of gussets.