  We study the stability of the BTZ black hole in the new massive gravity. This
is a nontrivial task because the linearized equation around the BTZ black hole
background is a fourth order differential equation. Away from the critical
point of $m^2 l^2=1/2$, this fourth order equation is split into two second
order equations: one describes a massless graviton and the other is designed
for a massive graviton, which could be obtained from the Fierz-Pauli action. In
this case, calculating quasinormal modes leads to confirm the stability of the
BTZ black hole. At the critical point, we derive two left and right logarithmic
quasinormal modes from the logarithmic conformal field theory. Finally, we
identify two $s$-massive modes propagating on the black hole background through
the conventional black hole stability analysis.
