  The growth of matter perturbations in the $f(R)$ model proposed by
Starobinsky is studied in this paper. Three different parametric forms of the
growth index are considered respectively and constraints on the model are
obtained at both the $1\sigma$ and $2\sigma$ confidence levels, by using the
current observational data for the growth factor. It is found, for all the
three parametric forms of the growth index examined, that the Starobinsky model
is consistent with the observations only at the $2\sigma$ confidence level.
