  In the case of a spatially flat Friedmann--Lema\^{\i}tre--Robertson--Walker
universe in $f\left( R\right) $-gravity we write the Wheeler-DeWitt equation of
quantum cosmology. The equation depends on the functional form of $f\left(
R\right) $. We select to work with four specific functions of $f\left( R\right)
$, in which the field equations for the classical models are integrable and
solvable through quadratures. For these models, we determine similarity
solutions for the Wheeler-DeWitt equation by determine Lie-B\"{a}cklund
transformations. In addition we show how the classical limit is recovered by
the similarity solutions of the Wheeler-DeWitt equation.
