The Ministry of Education of Korea has adopted the High School Credit System(HSCS) in order to improve the quality of high school education. The HSCS intended to provide students with individualized and flexible curriculum to support their sound and seamless growth, and under the HSCS, it is important to provide students as various subjects as they need. To this end, it is necessary to consider the supply and demand of teachers who have teaching certificates with adequate subjects. Considering the issue, this study aimed to explore the possibility of broadening a range of high school electives. Specifically, this study examined current subjects taught by high school teachers and their perceptions of teaching additional subjects. Teacher survey was conducted in the 82 sample and leading high schools of the HSCS and in total 1,333 teachers completed the survey questionnaire. Findings indicated that a large number of teachers had teaching certificates which allowed them to teach only one subject and those teachers taught subjects within subjects presented in their teaching certificates. The teachers reported, however, that they taught additional subjects from general education which were not directly related to subjects in their teaching certificates. In addition, teachers showed only modest intention to teach additional subjects and in order to teach additional subjects, they expected enough time to prepare more than additional teacher training. Based on the findings of the study, policy implications were suggested.