  The hadronic tau decay $\tau^- \to \nu_\tau \eta \pi^- \pi^0$ occurs through
V-A weak current. In this decay mode, the vector current contribution is
intrinsic parity violating and the axial current contribution is G parity
violating. The latter contribution is suppressed due to tiny isospin breaking.
We have computed both vector and axial vector form factors using a chiral
Lagrangian with vector mesons including the effect of isospin breaking and
intrinsic parity violation. A numerical result of the invariant mass
distribution is shown and the structure of $\rho$ resonance can be seen in the
distribution with respect to $M_{\pi^- \pi^0}$.
