PURPOSE: To produce the titled substance useful as an industrial raw material, in improved cultivation productivity, at a lowered production cost, economically in an industrial scale, by carrying out the first-stage cultivation mainly for the production of only the microbial cells, and the second-stage cultivation mainly for the produciton of xanthan gum.

CONSTITUTION: The objective xanthan gum is produced by carrying out (A) the first-stage cultivation mainly for the production of microbial cells of a xanthan gum-producing strain (Xanthomonas campestris) in a medium containing carbon source, nitrogen source, trace heavy metals, ≤100ppm phosphate ion and ≤100ppm magnesium ion, and (B) the second-stage cultivation mainly for the production of xanthan gum in a medium containing carbon source, ≥100ppm phosphate ion and ≥100ppm magnesium ion.