GPS on permanent stations has proved to be a powerful tool in crustal movement studies, capable to detect small trends of movement in a frication of time that required by the classical methods. Using three years data collected from fifty GPS permanent stations in South Korea the vertical velocity was determined. The constrained network adjustment technique was used in the adjustment step in-order to minimize the common mode signal effect, which is clearly found in the precise point positioning solutions. The obtained results show that the average vertical velocity in the Korean peninsula is 1.3 mm/year.