The cheese whey is an abundant residue obtained during the cheese processing and its disposal in the environment causes several drawbacks. The bioconversion of this by-product in added-value products is an important alternative to overcome this environmental problem. In this work, the feasibility of using cheese whey as carbon source for xanthan gum production was investigated using two strains of Xanthomonas campestris. The cheese whey:sucrose ratio and the supplementation of the medium were investigated by a Central Composite Design (CCD) in order to improve the xanthan gum production. Maximum xanthan gum productions were observed after 72 h using cheese whey as sole carbon source, 0.1% (w/v) MgSO4 x 7H(2)O and 2.0% (w/v) of K2HPO4, yielding approximately 25 g L-1. This value is quite higher than some results presented in the literature using glucose as substrate. Although the production was similar for the two strains, chemical composition and ionic strength presented several differences in chemical characteristics between the polysaccharides produced. (c) 2008 Elsevier Ltd. All rights reserved.