Abstract: The thermodynamic stability of tannin extract solutions has influence on tanning properties of the extracts, including penetrability, filling ability and fixation to the collagen fibre. In this study, thermodynamic stability of six extract solutions under different storage time, temperature and pH value, was investigated by dynamic light scattering (DLS). Some parameters, including Zeta potential, Z-average size of colloidal particles, and polydispersity index (PDI), were measured by Zetasizer Nano ZS series instrument. The results show that storage time has little influence on the stability of the extract solutions. Except Ternstroemia gymnanthera Sprague, for other extracts, the higher the temperature, the larger the colloidal particles are. Zeta potentials fell with the increase of temperature. The pH value has the strongest influence on stability. On the whole, solutions of condensed tannin extracts are much more stable toward pH value, temperature and storage time than those of hydrolysable tannin extracts.