  Kitaev physics has recently attracted attention in condensed matter for its
anticipated novel quantum spin liquid state. The thermal transport measurement
is crucial for probing the novel features of charge-neutral quasiparticles. In
this letter, we report a significant thermal Hall effect in $Na_2Co_2TeO_6$
(NCTO), a Kitaev quantum spin liquid candidate, when the magnetic field is
applied along the out-of-plane direction of the honeycomb plane. The thermal
conductivity ($\kappa_{xx}$) and thermal Hall conductivity ($\kappa_{xy}$) in
NCTO reveal distinct magnetic field dependences below and above the Neel
temperature ($T_N$) of 27 K. For $T>T_N$, $\kappa_{xx}$ has a monotonic
decrease in the field dependence, while $\kappa_{xy}$ persists up to $T^*$ =
150 K. On the other hand, both $\kappa_{xx}$ and $\kappa_{xy}$ exhibit complex
field dependence for $T<T_N$.
