The undrained shear strength of soil is one of the most important parameters required for geotechnical design. Depending on the design situations, the undrained shear strength of soil may have to be determined by different tests. In this paper, some testing data on the determination of the undrained shear strength of a residual soil in Singapore are presented. A series of tests including Ko consolidated undrained triaxial compression and extension tests, and Ko consolidated undrained direct simple shear tests have been conducted on large block undisturbed soil samples taken from the construction site ofT-06 (Queensway Tunnel) of the Deep Tunnel Sewerage System Project in Singapore. The anisotropic shear strength' behavior of the soil is discussed using the test data. The cu/crvo' against OCR relationships between different tests are established for practical applications.