Abstract: Rubber trees (Hevea brasilieasis Muell-Arg.) like other tropical trees, are very sensitive to chilling temperature. It may cause metabolic disturb ances and make severe injuries to the tree. The ecophysiological indices introduced in this paper are transpiration rate, osmotic pressure, pretoplasmic viscosity, protoplasmic permeability and water content. These indices can be used to estimate relative cold resistance of different clones or individual rubber seedlings. The results our measurements are summarized in the following table.