Fission fragment mass and kinetic energy distributions and mass-versus-energy correlations have been measured for the thermal neutron induced fission of 231Pa. The global mass distribution and the mass distribution for selected kinetic energy events show fine structure with a mean period of ≈ 2.5 amu. The peak/valley ratio of the mass distribution is 2271 ±854 compared to 554±31 for 235U. The dip △Ek dip values at symmetric fission for 231Pa and 235U are 14.8±4.2 and 20.6± 1.1 MeV respectively. The < Ek >(μh) for μh ≈ 125-135 is flatter than for 235U.