The present invention discloses a process for the production of chondroitin sulphate with an average molecular weight (Mw) of 10-30 kDa by chemical sulphation starting from an unsulphated chondroitin backbone, obtained in turn by acid hydrolysis of 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, unlike the sulphation obtained with the synthesis methods described to date.