Polysuccinimide, polyaspartic acid and salts of polyaspartic acid may be prepared by means of heating aspartic acid in the presence of sodium bisulfate. The molecular weight of the polymers may be increased from that obtained without the use of sodium bisulfate. The polysuccinimide, polyaspartic acid or salt of polyaspartic acid obtained have low color. Polyaspartic acid may be obtained in this manner directly from the effluent of an immobilized cell or enzyme column which catalyzes the production of L-aspartic acid without the necessity of intermediate isolation steps.