The aim of this written work is to make an evaluation system for exceptional trees in Slovenia, which will use objective criteria and standards as much as possible and take into consideration a great variety of natural phenomena in Slovenia, i.e. differences concerning the tree species, other special characteristics of trees, environment and socio-historical factors. We have analyzed measurements of the trees, which are part of natural heritage and their description following the evaluation criteria stated in the Nature conservation act. The use of these criteria differs widely from one evaluationto another. Space analysis has shown an uneven disposition of the heritage trees in Slovenia. A survey has been carried out among the forest experts from the Slovenia Forest Service about the exceptional trees and heritage trees in Slovenian forests. A new system of evaluation of exceptionaltrees has been proposed based on the following criteria: exceptional thickness, height, tree form, and complexity of interrelation, rarity, importance of the trees for the ecosystem, their role as witnesses andtheir aesthetic importance. Each criterion has its own evaluation standards. The system has been tested on exceptional trees registered at the Slovenia Forest Service, the Postojna regional unit. Numerous suggestions are stated in this work for a more objective and holistic approach to evaluation, conservation and protection of the exceptional trees and heritage trees in Slovenia.