Most of the biothickeners in current use by food industry are polysaccharides from plants (e.g. starch, pectin, locust bean gum, guar gum) or seaweeds (carrageenan, alginate). Because most of the plant carbohydrates used, need some form of chemicall modification ,therefore microbial exopolysaccharides (EPS) as an alternative class of biothickeners has atracted interest of many researchers in recent years. Microbial exopolysaccharides are biothickeners that can be added to a wide variety of food products, where they serve as viscosifying, stabilizing, emulsifying or jell agents. Since most lactic acid bacteria (LAB) are food-grade microorganisms with GRAS status (Generally Recognized As Safe), the use of the secreted EPS as natural alternatives to produce all-natural food products without additives from LAB has received increased attention. The aim of this study was to determine the optimum conditions for EPS production by L. rhamnosus to achieve maximum EPS production. Potential of four strains of L. rhamnosus ( Lr M2, Lr 519, Lr GG, Lr 7469) were determined for their ability for EPS production in Sucrose -Man Rogosa and Sharpe (Su-MRS) medium. The highest amount EPS was obtained for strain Lr 519. To enhance EPS production by Lr 519, the ability of Lr 519 for EPS production in skimmed milk and MRS medium were studied. The EPS production by Lr 519 in skimmed milk was higher than that in the MRS medium. In second stay of study to investigat the influence of carbon source on EPS production, sucrose, glucose and lactose were added at concentration 20 g/L to skimmed milk culture. The EPS production by Lr 519 in skimmed milk enriched with sucrose was higher than that in presence of skimmed milk contaning other sugars. To investigat the influence of nitrogen source on EPS production, yeast extract, yeast nitrogen base(YNB), peptone and tryptophan were added at concentration 20 g/L to skimmed milk cultures. The EPS production by Lr 519 in skimmed milk enriched by yeast extract and YNB was higher than that in skimmed milk enriched of other nitrogen sources. In this study a polysaccharide-free nitrogen source, YNB, was chosen to avoid interference of compounds found in yeast extract that interfere with EPS purification and quantification. To determine the optimum conditions for EPS production by Lr 519 in skimmed milk medium, the influence of combined effects of sucrose and YNB concentrations, incubation time and pH on EPS production during batch cultures was tested with a central composite design (CCD) using a response surface methodology (RSM). A significant relationship was observed between all factors (linear and squared) and EPS production except YNB concentration which did not have a linear effect on EPS production . The highest EPS concentration (248 mg/L) was obtained at incubation time of 60