A purified water-soluble fraction (ICP5) of a polysaccharide, isolated from a local Maori mushroom Iliodiction cibarium in New Zealand, was investigated for its structural properties. Size exclusion chromatography and dynamic light scattering showed that ICP5 had a large MW of 1.6 × 10(5) Da with a hydrodynamic diameter of 83 ± 8 nm. Particle size measurements also displayed the tendency of ICP5 to aggregate when suspended in water. The results of GC-MS, FTIR and NMR analyses allowed some characteristics of the chemical structure of ICP5 to be determined. GC-MS results showed that ICP5 contained only glucose (81.61%), galactose (12.90%) and mannose (5.49%) monomers. The characterized fragment structures of ICP5 were found to be dominantly consisting of uronic acids, which formed a backbone containing 1,4-β-D-GlcpA. A small amount of unsaturated uronic acid also appeared to be present.