We first find Xanthomonas campestris N. K-01 which don't produce xanthan at 28℃ cansynthesize and secrete the xanthan under low temperature (4℃). Little string is the most minute unit of the secreted under low temperature. Many little strings ecreted by bacterium cell extend to form a wider xanthan fiber. When depart from cell, xanthan fiber either twine to form double helix of bundle together. They are both advanced structures of the xanthan strings. Xanthan secreted under 4℃ has the same chemical composition and structure as that under 28℃, but lower moleculer weight and lower pyruvate content.