We have made thermal expansion measurements to examine the characters of an ordered phase IV in the dense Kondo compounds Ce x La 1−x B 6 (x=0.75 , 0.70). For both compounds, expansion along the [0 0 1] direction and shrinkage along [1 1 1] with decreasing temperature have been observed in phase IV. These results indicate the lattice distortion from cubic to trigonal structure. A ferro-quadrupole ordering of O yz, O zx, O xy with Γ 5 symmetry is a probable candidate for the order parameter of the phase IV.