MnPS3 is a quasi-2D S = 5/2 antiferromagnet on a honeycomb lattice. Using an energy integrating neutron scattering technique, we have measured the structure factor S(k) of the instantaneous magnetic fluctuations. The temperature dependence of the correlation length xi follows the Kosterlitz-Thouless prediction with parameters that are consistently described by a Heisenberg system with inter plane coupling J'/'J = 1/405 and weak xy-anisotropy.