  The in-medium neutron-proton, proton-proton(neutron-neutron) scattering cross
sections($\sigma_{np}^{*}$, $\sigma_{pp(nn)}^{*}$) are studied based on QHD-II
type Lagrangian within the framework of the microscopic transport theory. The
results demonstrate that, for free nucleon-nucleon scattering cross sections,
the isospin dependence is dominantly caused by $\rho$ meson field. The medium
correction of nucleon-nucleon scattering cross sections is also isospin
dependent, $\sigma_{np}^{*}$ depends on the baryon density weakly and
$\sigma_{pp(nn)}^{*}$ depends on the baryon density significantly, which is due
to the different effects of the medium correction of nucleon mass and $\rho$
meson mass on $\sigma_{np}$ and $\sigma_{pp(nn)}$, respectively
