In the Korean mobile market, the mobile phone has reach the stage of maturity in terms of demand. Since the long-term evolution(LTE) service was introduced in 2011, there have been drastic changes in the market structure. The purpose of this paper is to examine the user intension of brand switching, to analyse the market share among 3 major mobile service companies using the brand switching matrix and to provide some insights. The results show that the smartphone subscriber rate provided by Ministry of Science, lCT and Future Planning agrees with the market share by brand switching matrix of this study. The potential rate of costumer retention would be arranges in order of SKT>KT>LGU+. The preference of mobile service company on switch be in order of SKT>KT>LGU+. The future market share be SKT 63.55%, KT 21.99%, LGU+ 14.36%. The potential rate of costumer retention fell sharply over the past year, suggesting the drastic fluctuations in market share for a while.