  The spontaneous breaking of chiral symmetry (SBCS) is one of the most
important phenomena of hadron physics. It defines the properties of all the
light mesons and baryons. The Chiral Perturbation Theory (ChPT) encodes QCD
hadronic correlators at low-energy region in the terms the low-energy constants
(LEC) -- the expansion parameters on light quark current masses $m$ and
external momenta $p$. The LEC's can be extracted from the phenomenology or from
QCD lattice calculations. On the other hand, QCD instanton vacuum/instanton
liquid model provides a very natural nonperturbative explanation of the SBCS.
It provides a consistent framework for description of the pions and thus may be
used for evaluation of the LEC. Our aim is to calculate the vacuum properties
and the LEC's within instanton vacuum model and confront with phenomenology and
lattice results.
