New series of tri-sulfated (iota-carrageenan) and tetra-sulfated (rho-carrageenan) carrageenans were prepared by the sulfating reaction from iota-carrageenan. The chain conformations of new carrageenans in aqueous solutions were investigated in the presence of various metal salts by means of static/dynamic light scattering and small-angle X-ray scattering, and their conformational characteristics were discussed with respect to the gelation behaviour. Although the overall conformation of newly prepared carrageenans is specified as a random coil, the local chain retains a rigid-rod-like structure by forming a helical conformation. The sulfate groups on C2 of (1-->3)-linked beta-D-galactoses were found primarily responsible to prevent gelation.