  We studied the transport properties of CeRu_2Al_10 single crystals. All the
transport properties show largely anisotropic behaviors below T_0. Those along
the a- and c-axes show similar behaviors, but are different from those along
the b-axis. This suggests that the system could be viewed as a two-dimensional
system. The results of the thermal conductivity and thermoelectric power could
be explained by assuming the singlet ground state below T_0. However, the
ground state is not simple but has some kind of structure within a spin gap.
