A process for the preparation of a chondroitin sulphate salt with an average molecular weight (Mw) of 10-30 kDa via chemical sulphation of an unsulphated chondroitin backbone is provided. The unsulphated chondroitin can be obtained by acid hydrolysis of a capsular polysaccharide K4 made directly from E. coli strain O5:K4:H4 or directly produced from a genetically modified strain of E. coli. Sulphation of the N-acetyl-D-galactosamine residue at position 4 or 6 takes place simultaneously in the same polysaccharide chain, simulating the sulphation pattern observed in natural chondroitin sulphate.