Biodegradable polymers and the hydrogels have been increasingly applied in a variety of biomedical fields and pharmaceutics. alpha,beta-Poly(N-2-hydroxyethyl-DL-aspartamide), PHEA, one of poly(amino acid)s with hydroxyethyl pendants, are known to be biodegradable and biocompatible, and has been studied as an useful biomaterial, especially for drug delivery, via appropriate structural modification. In this work, hydrogels based on PHEA were prepared by two-step reaction, that is, the crosslinking of polysuccinimide, the precursor polymer, with oligomeric PEG or PEI-diamines and the following nucleophilic ring-opening reaction by ethanolamine. Soft hydrogels possessing varying degrees of gel strength could be prepared easily, depending on the amount of different crosslinking reagents. The swelling degrees, which were in the range of 10-40 g-water/dry gel, increased somewhat at higher temperature, and also at alkaline pH of aqueous solution. A typical hydrogel remained almost unchanged for 1 week, at 37degreesC in phosphate buffer of pH 7.4, and then seemed to degrade slowly as time. A porous scaffold could be fabricated by the freeze drying of water-swollen gel. The PHEA-based hydrogels have potential for useful biomaterial applications including current drug delivery system. (C) 2003 Wiley Periodicals, Inc.