In CeFe2, CeCo2 and CeNi2 below 100 K, measured values of the lattice constant, thermal expansion coefficient, intensities of X-ray diffraction lines (hkl) and resistivity exhibit similar anomalies which are closely correlated with the valence variation of the Ce ion. The intensities of the diffraction lines in the CeCO2 and CeNi2 samples suggest that these substances can be considered as a combination of two MgCu2 structures with two different lattice constants a1 and a2 (a2