Objective To develop a method for rejuvenating Sreptococcus pneumoniae serotype 19F(PN19F) and optimize the purification process of capsular polysaccharide.Methods Liquid amplification medium and solid selective medium for PN19F were prepared for screening single colonies with thick capsule.The fermentation of PN19F before and after rejuvenating as well as the yield and quality of purified polysaccharides were compared.The fermentation liquid was lysed and subjected to acid precipitation for 8,24 and 48 h,then purified by 100 KD ultrafiltration to obtain polysaccharides by ethanol method and freeze-drying method resp.The polysaccharide harvest,component test result,antigen activity and ∼1H-NMR were compared.Results The A600 value and culture time of fermentation harvest of PN19F before and after rejuvenating showed no significant change.After purification,the yields of purified polysa-ccharides were 0. 2 and 0. 6 g/L resp.,which increased by 195% as compared with those before rejuvenating.The polysaccharides after purification by acid precipitation for 8 and 24 h were qualified,of which the yield after purification for 24 h was about 38% higher than that for 8 h.However,after acid precipitation for 48 h,the yield showed no significant change,while the polysaccharide quality was unqualified.All the indexes of purified polysaccharides prepared by ethanol method and lyophilization method were qualified,which showed no significant difference.Conclusion PN19F strain rejuvenated by two media increased the yield of polysaccharide singificnatly.The acid precipitation time was less than 24 h.Both ethanol method and lyophilization method may be used for the preparation of purified polysaccharide.