The present invention relates to the synthesis of D-chiroinositol from a dialdose, comprising the steps of condensing the dialdose by an acyloin condensation reaction to form an inosose, protecting the carbon atoms at the 2, 3, 4 and 5 positions, reducing the ketone of the inosose and removing the protecting groups. In addition, a method of preparing mannodialdose from mannuronic acid is disclosed.