Thermal analysis, with DSC and TGA of fusion and decomposition processes of some quinoline compounds were carried out to determine their stability. The quinoline compounds are classified by the R-6 sustituent: No-2, NHCOCH3, H or OCH3 and they have a variable substitution in position 1. Certain factors in the substitution (length of chain, chain branching and unsaturation) are not especially relevant to the physical stability. The compounds are very polar and the dipole-dipole forces give stability to the crystal. An increase in the physical stability is also observed with aromaticity and when halogens are present. An increase in the chemical stability, from the acetylamine group to the nitro group, is observed. (C) 2004 Elsevier B.V. All rights reserved.