  By assuming that the $f_0$ and $a_0^0$ mesons are mixed states of the
two-quark - tetraquark, the mixing angle between them is estimated within QCD
sum rules method, and it is obtained that the mixing angle is $(6.03 \pm
0.08)^\circ$. Our prediction on mixing angle can be checked in further
experiments which can shed light on choosing the "right" structure of $f_0$ and
$a_0^0$ mesons.
