A statistical methodology, combining Plackett-Burman design (PBD) with uniform design (UD), was applied to optimize the concentrations of different inorganic salt components in liquid fermentative medium for carotenoids production by Rhodobacter sphaeroides. Among eleven inorganic salts investigated with PBD, MgSO4, Na2HPO4, FeSO4 and Na2CO3 were selected out based on their statistically significant (P < 0.05) and positive effects on carotenoids yield. UD was used for further optimization of those selected inorganic salts in order to increase carotenoids output. By step-wise analysis to the data from UD, a second-order polynomial model was established to identify the relationship between the carotenoids output and these four inorganic salts. The optimum combination of inorganic salts for carotenoids yield was evaluated with the nonlinear optimization algorithm as follows: MgSO4 0.12 g/L, Na2HPO4 2.05 g/L. FeSO4 0.03 g/L, Na2CO3 2.22 g/L, and the other components of fermentative medium were kept the same as basal medium (citric acid 8.1 g/L, NH4Cl 3.5 g/L, corn syrup 1.8 g/L). A maximum carotenoids yield of 17.245 mg/L was demonstrated by confirmatory experiment to the Optimum medium in 5-day fermentation. (c) 2006 Elsevier Ltd. All rights reserved.