  We study the level spacing statistics $P(s)$ and eigenstate properties of
spinless fermions with Coulomb interaction on a two dimensional lattice at
constant filling factor and various disorder strength. In the limit of large
lattice size, $P(s)$ undergoes a transition from the Poisson to the
Wigner-Dyson distribution at a critical total energy independent of the number
of fermions. This implies the emergence of quantum ergodicity induced by
interaction and delocalization in the Hilbert space at zero temperature.
