The present invention relates to process for reducing the endotoxin content of a sample of fermentation broth containing polysialic acid and endotoxin comprising the sequential steps: (i) adding to the sample a base having a pKa of at least 12 to form a basic solution having a pH of at least 12, incubating the solution for a pre-determined time at a pre-determined temperature； and (ii) recovery of PSA, suitably by (iii) passing the sample through an anion-exchange column whereby polysialic acid is absorbed on the ion exchange resin； (iv) washing the column with one washing buffer, whereby polysialic acid remains absorbed on the ion exchange resin； and (v) eluting the polysialic acid from the column using an elution buffer to provide a product solution of polysialic acid having reduced endotoxin content.
