A model for kinetics of circular substrate cleavage by restriction endonuclease was formulated. The aim of the analysis of the model was to extract kinetic constants for all target sites from time-dependence of fragment concentration in reaction products. That was proved to be possible for molecules with an odd number of fragments only. A symmetry of the molecules with an even number of fragment is the cause. A solution for molecules with an odd number of fragments was found and methods for dealing with the other molecules were suggested.