The flow properties of the polysaccharides produced by Haloferax mediterranei(T) ATCC 33500 and its super mutant Haloferax mediterranei EPS++, R4 and EPS++ respectively, were investigated. The R4 repeating unit is a trisaccharide containing mannose and 2-acetamido-2-deoxyglucuronic acid, ester sulphate groups are also present. In order to compare the properties of both polymers viscosimetric measurements were carried out at different integration times and using different concentrations of polymer. Under the assayed experimental conditions no effect of the time applying stress is detected for either polymer. A strong pseudoplastic behaviour is observed which is increased as the polymer concentration rises. Differences in viscosity between both polymers are due to the different molecular weights. The correlation of the experimental data using a modification of the Cross model has given very good results.