The flat Dilatometer test(flat DMT) designed and proposed by Marchetti in 1975 to characterize the properties of soil has been known as an in-situ testing method which is simple and robust to use, and reliable for site stratification and evaluation of soil properties. There are many researches that have been done to evaluate the horizontal coefficient of consolidation from the dissipation test results of flat DMT on normally consolidated and slightly overconsolidated clays. The representative estimation methods of estimating the horizontal consolidation coefficient are DMT-C method which uses C-reading dissipation curve and DMT-A method which uses A-reading dissipation curve. This paper represents a comparison analysis of those two methods in obtaining horizontal coefficients of consolidation for Korean marine clays. The reference values are also obtained from CPTU or consolidated undrained tests. Finally, the applicability of using flat DMT to characterize the consolidation behavior for Korean marine clays is reviewed.