  Nonreciprocal charge transport phenomena are widely studied in
two-dimensional superconductors, which demonstrate unidirectional-anisotropy
magnetoresistances as a result of symmetry breaking. Here, we report a strong
nonreciprocal transport phenomenon in superconducting CsV$_{3}$Sb$_{5}$ thin
flakes. The second harmonic voltages, mainly originating from the rectification
effect of vortex motion, are unambiguously developed with in-plane and
out-of-plane magnetic fields, and their magnitudes are comparable to those in
noncentrosymmetric superconductors. The second harmonic magnetoresistances
split into several peaks and some of them reverse their signs by ramping the
magnetic field or the current within the superconducting transition. The
nonreciprocity suggests a strong asymmetry in CsV$_{3}$Sb$_{5}$. The
centrosymmetric structure and symmetric electronic phases in CsV$_{3}$Sb$_{5}$
can hardly induce the distinct nonreciprocal transport phenomenon, which could
be correlated to a symmetry breaking from an unconventional superconducting
order parameter symmetry.
