Thirteenp-n-alkoxybenzylidene-p-aminobenzoic acids were prepared and their mesomorphic transition temperatures were determined. They exhibit mesophases of greater relative thermal stability than thep-n-alkoxybenzoic andp-n-alkoxycinnamic acids but 4′-n-alkoxydiphenyl-4-carboxylic acids exhibit greater thermal stability than the acids studied here thoughp-n-alkoxybenzylidene-p-aminobenzoic acids are longer by -CH+N- group in the monomer; this may be attributed to the stereochemistry of -CH+N- link causing the molecule to be broader than the 4′-n-alkoxydiphenyl-4-carboxylic acids. Comparatively higher thermal stability of mesophases of these acids is emphasized by the mesomorphic behaviour of methylp-n-alkoxybenzylidene-p-aminobenzoates which are purely smectic and the absence of anisotropic melt in the analogousp-n-alkoxybenzoates.