The invention provides a method for releasing capsular polysaccharide from S.aureus type 5 or type 8 cells, comprising the step of treating the cells with acid. The invention further provides a process for purifying capsular polysaccharide from S.aureus type 5 or type 8 cells comprising this method. Other processing steps may be included in the process, such as enzymatic treatment, e.g . to remove nucleic acid, protein and/or peptidoglycan contaminants； diafiltration, e.g. to remove low molecular weight contaminants； anion exchange chromatography, e.g. to remove residual protein； and concentration.
