The purpose of this study was to explore key kinematic variables of Yeo Seojeong vault by analysing series of vaults performed by Yeo Seo Jeong (YSJ) in order to provide technical support for YSJ and coaches to develop successful training strategy as well as promote adoption of the technique among gymnasts. Two-dimensional video recordings of YSJ during 2019 Korea Cup (1 successful vault) and practice session (3 unsuccessful vaults) were taken. Phase time, changes in position of body centre of mass, velocity of body centre of mass, and changes in various joint angles, and changes in angular velocity were subjected to kinematic analysis. Kinematic analysis revealed that successful vault was possible when YSJ had fast horizontal velocity at horse touch down as well as fast trunk rotation during horse contact, these allowed her to have faster thigh rotation and take-off angle exceeding 90 degrees at horse take-off resulting to reach maximum height and the length during post-flight. Together with higher and longer post-flight, faster rotation and twisting warranted the successful completion of Yeo Seojeong vault. From the unsuccessful vaults, we found that slow horizontal velocity and bent body posture at board contact as well as low body COM, small horizontal displacement of body COM, and slow vertical velocity at every preparation phase had adverse effect on the horse take-off, i.e. improper blocking, weak propulsion. These resulted rather insufficient post-flight with deceleration of rotation and twisting in descending phase of post-flight leading to insecure landing.