Mesogenicity of five cyclotriphosphazenes and two cyclotetraphosphazenes with a similar dodecyl or dodecyloxy end and different central hard groups was studied. In the four cyclotriphosphazenes except for a cyclotriphosphazene with phenyl derivative side chains, enantiotropic mesomorphic phases were observed. The order of the thermal stability in mesophase is phenylazobenzene > phenyliminomethylphenyl > biphenyl groups for the side chains. The cyclotetraphosphazenes with biphenyl and Schiff base derivatives have lower mesomorphic thermal stability than cyclotriphosphazenes with the same side groups.