The present invention relates to certain polyphenol(s) having adjuvant property that can be used for the vaccine preparation. Also, the current invention provides adjuvant system comprising said polyphenol(s) and delivery system such as an immunostimulating reconstituted influenza virosomes (IRIVs). The present invention illustrates the said polyphenol(s) or an adjuvant system comprising of such polyphenol(s) and IRIVs can provide better level of immune response against antigen of interest than conventional vaccine systems. The preferred polyphenol according to the present invention can be beta-sitosterol. Beta-sitosterol can be optionally combined with the known adjuvant(s) to enhance immune response.