The Old Alluvium of Singapore is studied using both laboratory and field tests to investigate its engineering properties. The natural heterogeneity of OA is recognized and a classification system developed. Sampling effect, Ko and shear strength were studied in detail. It is found the clay content and stress history helps OA to resist sampling disturbance. However, the current commonly used thick-wall samplers need to be improved. Ko values of normally consolidated OA can be predicted by Jakya??s equation, but the over-consolidation stress history resulted in scattered Ko values due to different OCR values and soil composition.A new concept, granular void ratio equivalent ege, is developed by assigning different contribution factors to different fines. Strength and stiffness of OA is governed by granular void ratio equivalent ege rather than the void ratio e. The importance of understanding the mineralogical composition and stress history in characterization of natural soils is highlighted.