The reaction of poly(succinimide) (PSI) with dodecylamine (DDA) in DMF produced a partially dodecylamine-modified poly(succinimide) (DDA-PSI). When the mole ratio of the DDA units and the succinimide units in PSI (M-w = 22,000) varied from 0.1 to 0.5 in the feed, the mole fraction of the N-dodecyl aspartamide units in PSI increased from 4 to 46 mol-%, and the M-w of DDA-PSI was almost constant at M-w = ca 20,000. Sodium DDA-modified poly(aspartate) (DDA-PASP-Na) was obtained in high yield by hydrolysis using NaOH solution. DDA-PASP-Na exhibited biodegradability (14 similar to 21 %) and a high MnO2-dispersion property (10.3 g-MnO2 / g-polymer).