  We study macroscopic quantum tunneling (MQT) in c-axis twist Josephson
junctions made of high-T_c superconductors in order to clarify the influence of
the anisotropic order parameter symmetry (OPS) on MQT. The dependence of the
MQT rate on the twist angle $\gamma$ about the c-axis is calculated by using
the functional integral and the bounce method. Due to the d-wave OPS, the
$\gamma$ dependence of standard deviation of the switching current distribution
and the crossover temperature from thermal activation to MQT are found to be
given by $\cos2\gamma$ and $\sqrt{\cos2\gamma}$, respectively. We also show
that a dissipative effect resulting from the nodal quasiparticle excitation on
MQT is negligibly small, which is consistent with recent MQT experiments using
Bi${}_2$Sr${}_2$CaCu${}_2$O${}_{8 + \delta}$ intrinsic junctions. These results
indicate that MQT in c-axis twist junctions becomes a useful experimental tool
for testing the OPS of high-T_c materials at low temperature, and suggest high
potential of such junctions for qubit applications.
