Macromolecular alginate extracted from brown seaweeds was treated with acid to generate mannuronate blocks. The resulting polymannuronates were degraded by hydrogen peroxide with a procedure optimized for obtaining high recovery of low molecular weight saccharides. The resulted mixture of different sized oligomannuronates was separated by gel chromatography on a Bio-gel P-4 column and Mono Q column. The purified oligomers were characterized by anion-exchange HPLC as well as spectrum analysis. This report provides a general procedure for generation and purification of oligomannuronates with in the size of 2-7 sugar units from alginate.