New retailers, especially giant retailers, so called "mart" or "discounter" which introduced around 1996, when Korea's domestic retail market was opened to the world, have brought big transitions. Consequently, new comers like discounters and CVS drove out department stores, mom & pops and traditional retailers. Literatures showed two reverse opinions for the giant retailers; rising consumers' benefit, or dropping small retailers' businesses. This study have conducted to find the situation of market concentration in retail market, and to learn the new market condition in it. According to the study, in 2005, CR3's of Korea's whole retail industry was counted 12.8%, and CR5 of that was 13.9%. CR3 of discount store business was 39%, department stores' 55%, and TV home shopping businesses' was 75%. In addition to those results, indices growing worse. So, we can say this industry already get into the oligopolistic industrial organization. Generally, under monopolistic or oligopolistic market structure, consumers' benefit may shrink and businesses' surplus profit may jump. So, it means, it's good time to turn government's policy for the retail industry in Korea to fair competition policy instead of development policy.