Structural changes and folding properties of 2- and 3-dimensional di-block polyampholytes are investigated via multicanonical molecular dynamics simulations. The restricted free energy of the 2-dimensional system clearly shows double well structure at intermediate temperature region, which is indicative of the structural transition between extended and compact structures. In the 3-dimensional system, only single well structure in the restricted free energy is observed. ©2000 American Institute of Physics.