  Topological insulators are emerging materials with insulating bulk and
symmetry protected nontrivial surface states. One of the most fascinating
transport behaviors in a topological insulator is the quantized anomalous Hall
insulator, which has been observed inmagnetic-topological-insulator-based
devices. In this work, we report a successful doping of rare earth element Tb
into Bi$_{1.08}$Sb$_{0.9}$Te$_2$S topological insulator single crystals, in
which the Tb moments are antiferromagnetically ordered below ~10 K. Benefiting
from the in-bulk-gap Fermi level, transport behavior dominant by the
topological surface states is observed below ~ 150 K. At low temperatures,
strong Shubnikov-de Haas oscillations are observed, which exhibit 2D-like
behavior. The topological insulator with long range magnetic ordering in rare
earth doped Bi$_{1.08}$Sb$_{0.9}$Te$_2$S single crystal provides an ideal
platform for quantum transport studies and potential applications.
