An acidic mucilage was isolated from the outer-layer seed coat of shaddock (Citrus grandis Osbeck) by water extraction at room temperature, and purified by DE-52 anion-exchange chromatography using 0.26  0.37 M NaCl. This purified mucilage was almost entirely composed of galacturonic acid residues. Glycosyl-linkage analysis showed that the backbone was 14 linked. Fourier Transform Infrared Spectroscopic analysis and determination of the degree of methylation further revealed that the mucilage was a low-degree (11.94%) esterified homogalacturonan. Size exclusion chromatography showed that the major molecular weight distribution of 610.9 kDa.