In order to cope with the recent fuel efficiency and exhaust emission regulation of vehicles, vehicle weight reduction has become an indispensable item rather than an option. Domestic and overseas automakers are continuously conducting research to address these lightweight issues. Among these methods for weight reduction, the application of high-strength steel with a relatively low price and lightweight effect is increased. Strength is improved when the material is replaced with high-strength steel; however, it is difficult to expect stiffness improvement to enhance the driving safety required for the automobile. In this paper, the study on stiffness improvement through the finite element analysis and the test evaluation of stiffness according to the application of high-strength steel body part are carried out. It is also confirmed that the stiffness improvement according to the application of high-strength steel is only possible through structural optimization.