In this study, effects of size and direction on mechanical properties of thinned single crystal silicon wafer are investigated by the direct tensile test. The silicon wafer is {001} and femtosecond laser patterning is used for fabricating dog-bone specimens for uniform stress distribution in gauge length. Mechanical properties of specimens with a thickness of 10, 20, 50, and 100-μm and with a direction of , , , and are measured to identify effects of size and direction, respectively. Young's modulus of thinned single crystal silicon wafer was constant while strength increased, as the thickness decreased. When the direction changed, each direction of the thinned silicon wafer has its inherent Young's modulus, and the experimental data fitted well with the theory of anisotropic elasticity.