This study is intended to analyze the factors that have an effect on occupational achievement of Korean high school graduate youths, especially focusing on the utility of social network from the perspectives of social capital theory. It laid great emphasis on the construction of an alternative analytical framework for the relation between social capital and occupational achievement using comparative analysis of the effects of the personal network and institutional network. The results are as follows: High school graduate youths have been getting jobs through the personal networks, such as friends, seniors, juniors, parents, and relatives. Personal networks led to much higher School-to-Work Transition than any other way of seeking work. However, when I finished analyzing how each type of network affects the Transition from School-to-Work, I found that the most important way of seeking work in the aspect of effectiveness is not the personal network nor any other ways but the institutional network. Therefore, I conclude that the institutional network variables, such as school recommendations, is the most powerful resource for School-to-Work Transition. Institutional network variables have a substantial effect on occupational achievement even with the other individual variables and the labor market variables under control. In conclusion, it can be expected that a lot of job opportunities and occupational achievement can be given to high school graduate youths by building up and strengthening the institutional network through making close connection between schools and companies.