The effective bending strength determined by the elastic buckling of constituent members for three-way doublelayer lattice plates is derived, considering the effects of the dimensions and connecting elasticity of joints. The strength is expressed as a surface in the Mx-My-Mxy space, and its property is discussed varying the rate of the bending rigidities of chord and web members for some dimensions of joints. The strength is compared with that of the pin-jointed truss of the same members. This rate is between zero and four, and usually larger than unity when the jointing rotational spring constant is several times larger than the bending rigidity per unit length of bars, EI/l.