Biodegradable alginate-derived polymeric surfactants (APSs) with a linear alkyl group (C8, C12, C16) were synthesized by oxidation followed by reductive amination of 2,3-dialdehydic alginate. The oxidized alginates and all APSs were characterized by spectral and X-ray diffractometry analysis. The sonicated suspension test was employed to form self-aggregates in aqueous solution. In the case of 40% CHO-C8 APS, the lowest interfacial tension, 31.5 mNm(-1) was obtained at the c.m.c. value of 1.35 g L-1. A biodegradability test on the 30% CHO-C12 APS system suggested that it would be attacked by a soil microorganism, Aspergillus niger.