  We study theoretically weak localization of excitons in atomically-thin
transition metal dichalcogenides. The constructive interference of excitonic de
Broglie waves on the trajectories forming closed loops results in a decrease of
the exciton diffusion coefficient. We calculate the interference contribution
to the diffusion coefficient for the experimentally relevant situation of
exciton scattering by acoustic phonons and static disorder. For the acoustic
phonon scattering, the quantum interference becomes more and more important
with increasing the temperature. Our estimates show that the quantum
contribution to the diffusion coefficient is considerable for the
state-of-the-art monolayer and bilayer transition metal dichalcogenides.
