In this paper, the shear response of three-dimensional micro-lattice structures was investigated based on numerical stress analysis, FEM. The mechanical properties strongly depend on the number of unit cell in three directions x,y,z, and for a flat structure (number of cells in y-direction Ny=1), the deformation pattern observed in the structure can be classified into two types. The shear modulus G*for a flat structure obtained by FEM can be estimated by the elementary beam theory with a good accuracy. Also, for a flat structure with slender struts, the collapse is occurred by elastic buckling, and that with relatively thicker struts, the collapse strength agrees well with the theoretical result. Moreover, for the case of the cubic structure, if the structure has the same number of unit cell in x- and z- directions (numbers of cells in two directions Nx=Nz=M), the shear modulus G* shows a unit curve regardless of the number M, so that the modulus can be estimated by using the curve for various cubic structures.