The present invention provides a process for preparation of highly purified mogrosides mixture from low purity mogrosides mixture. The process comprises providing a mixture of low purity mogrosides, dissolving the low purity mogrosides mixture in water or an aqueous alcohol solution to form an initial solution of mogrosides, passing the initial solution through a column system, wherein the column system comprises a plurality of columns, and each column is packed with a sorbent having different affinities to impurities and mogrosides so that one or more columns retains more mogrosides than other columns, washing the columns to remove impurities with an acidic aqueous solution, a basic aqueous solution, and an aqueous alcoholic solution successively, eluting the columns with an aqueous alcohol solution that contains higher alcohol content than the aqueous alcohol solution used in the washing step, wherein the eluate from the columns with high content of mogrosides are combined, and drying the combined eluate to obtain high purity mogrosides with the content of the total mogrosides are more than 70% (w/w). The present invention also provides a sweetener mixture and product comprising high purity mogrosides.