Abstract: Purified and substantially pure &bgr;-carrageenan and processes for their preparation. Purified &bgr;-carrageenan can be obtained from a marine macroalga containing &bgr;-carrageenan and/or a precursor thereof by the steps of: A. where the macroalga contains a precursor of &bgr;-carrageenan, reacting the macroalga with an alkaline compound to convert the precursor to &bgr;-carrageenan, B. extracting carrageenan from the macroalga, C. treating the extracted carrageenan with an aqueous quaternary ammonium salt to form a precipitate and an aqueous solution, D. separating the solution from the precipitate, and E. isolating purified &bgr;-carrageenan from the solution. Substantially pure &bgr;-carrageenan can be obtained from purified &bgr;-carrageenan by the further steps of: F. forming a solution of purified &bgr;-carrageenan in water, G. contacting the solution with an ion exchange agent that removes carrageenan which contains sulfate ester from the solution, H.