The smallest at most bimolecular chemical reaction system with Hopf bi
furcation is presented. First the notion smallest reaction system is e
xplained. Since the lowest number of intermediates has the highest pri
ority in this characterization and since it has already been shown tha
t three-component systems can have a Hopf bifurcation[1], the smallest
reaction system must contain three intermediates. On the basis of a s
ufficient condition for a Hopf bifurcation in three-dimensional system
s it is possible to find one reaction system which is according to the
given characterization, the smallest one. In the first part of this p
aper it is shortly pictured and in the second part a more extensive pr
oof that this system is really the searched smallest one is given.