In order to quantify the tendency to flow characteristics of sandy soils, the maximum value of excess pore water pressure ratio developed during undrained monotonic loading test was taken as an index property and defined as flow potential. Triaxial compression tests, triaxial extension tests and simple shear tests on Toyoura sand were conducted by means of conventional triaxial and hollow cylinder torsion shear apparatuses. As a result, it became clear that the flow potential of sand was greatly affected by shearing mode. Sand at the same density showed the lowest flow potential in triaxial compression and the highest in triaxial extension, while simple shear condition exhibited intermediate behavior. Flow potential was related to residual strength ratio and criteria for flow failure were developed. Evaluation of flow potential and behavior of ground from the N-value of SPT were also discussed.