High molecular weight polysuccinimide (PSI), as the precursor polymer for water-soluble poly(aspartic acid), was prepared by the thermal polycondensation of L-Aspartic acid. The molecular weight, estimated from the solution viscosity of the PSI, was within a range of 100000∼140000 Dalton. A crosslinked gel powder was prepared by the thermal curing reaction of a freeze-dried mixture composed of polyaspartic acid and a proper amount of PEG-diepoxide in water. The dependences of swelling behavior on the composition and curing conditions were also investigated.