Mekong Delta Clay and Bangkok Clay, the uppermost soil layers, were reviewed from soil formation, landforms, and geotechnical properties. This paper studied and compared the geological and geotechnical properties of Mekong Delta Clay and Bangkok Clay using secondary data from 20 boreholes in the Mekong Delta and more than 4,000 boreholes in Bangkok Clay. Data validation was examined for data normalization, possible, and statistical ranges. Some engineering properties are correlated to physical properties. The landforms of the Mekong Delta are classified into three types: back swamp/swamp, mangrove marsh, and sand dune close to the coastal zone. While Chao Phraya Delta mainly consists of marine deposits associated with an alluvial river fan at the edge. The results showed that Mekong Delta Clay's and Bangkok Clay's thicknesses were 4-22 and 3-30 m, respectively. Mekong Delta Clay contained silt-sized particles, whereas Bangkok Clay contained clay-sized particles predominantly. Physical properties indicated, for example, that Mekong Delta Clay had less plasticity (PI = 19.95%) than Bangkok Clay (PI = 42.26%). The overconsolidation ratio (OCR) of Mekong Delta Clay was normally consolidated to moderately overconsolidated clay (OCR = 1.04-7.99), while OCR of Bangkok Clay was classified as normally consolidated to lightly overconsolidated (OCR = 0.83-2.92). In addition, the compression index (Cc) showed that Mekong Delta Clay (Cc = 0.04-0.36) had much lower compressibility than Bangkok Clay (Cc = 0.51-1.54). These data will further serve as essential indexes for the Mekong Delta's sustainable development.