We studied the thermal property of metal complex salts (DMe-DCNQI)(2)Cu formed of DMe-DCNQI molecules of which some of hydrogen atoms are substituted by deuterium atoms. In those systems, we have discovered peaks in the specific heat originating from the orientation freedom of deuterated methyl groups. In systems containing methyl groups with one deuterium atom (CH2D), we found Schottky type of specific heat. In system with CHD2, we observed peaks not of Schottky type. To find out the origin and mechanism of these anomalies, we carried out the thermal study of the mixed crystals composed of molecules with CH2D and those with CHD2. We clarified the conformational ordering of CHD2 molecular along c axis in the DCNQI-Cu system.