This is a study of CHOK-DU-RI(族頭里) a black crown-like headpiece worn by woman on formal occasion in Chosun Dynasty and has succeeded until now. CHOK-DU-RI was originated by BOKTAK worn by Mongolian noblewomen and inflowed to the last period of Koryo dynasty under occupation of Yuan. The documentary records of O-JU-YON-MUN-CHSNG-JON-SAN-KO( by Lee Kyu-kung CHUNG-JANG-KWAN-JON-SUH by Lee Tock-mu and KO-SA-TONG by choe Nam-sun verify CHOK-DU-RI is a custom of mongolian fusion that was affected by KO-KO of Yuan and was formed. Ko-Ko is the same as BOKTAK. It is assumed KO-KO is a borrowed name as its transcription varies. The name was given according to its appearance which is certified by the record CHANGCHUN-CHIN-IN-SEO-BANG-YU-RAM-KI. It says that it can be simply named KO-KO as its edge is alike ad goose or a duck. In addition KO-Ko was called CHOGTAI in case of being added a camel fur that is JUGDUR. CHOGTAI similarily pronounced with CHOK-DU-RI which of being added a camel fur that is JUGDUR, CHOGTAI similarily pronounced with CHOK-DU-RI which provd CHOK-DU-RI was originated in Mongol. The shape of BOKTAK is very high and wided toward the top with the top with the angle getting more pointed and a feather stuck on the side. But its height got lower and its size smaller as it did gradually Koreanized to a CHOK-DU-RI. The use of CHOK-DU-RI has been settled since the last period of Chosun Dynasty. It came to stay as a popular custom when King Young-jo and Jong-jo wanting to do away with the corrupt practice of KA-CHE encouraged women at that time to do their hairs with CHOK-DU-RI instead of KA-CHE. It is as follows the classification of CHOK-DU-RI. First classified by a use group is divided into ceremonial use such as the seven treasures CHOK-DU-RI and jeweled CHOK-DU-RI. Hereby it is assumed that CHOK-DU-RI was used regardless of fortune. Secondly it varies by its type of frame. There are SOM CHOK-DU-RI OHT CHOK-DU-RI and O-YOM CHOK-DU-RI a kind of SOM CHOK-DU-Ri formed a base of O-YOM-MO-RI. The third group by jeweling has WHE-BONG CHOK-DU-RI and TA-BONG-CHOK-DU-RI JEwele CHOk-DU-RI can be still seen being commercially lent and worn by the brides at nuptical ceremonies performed in tradition of fashion and when worn bya bride as she gives her parents to her parents-in-law.