---

Background and Objective: Many studies have been performed on the effect of various parameters on the rheological behavior of gums. Gums are used in food products because of their functional characteristics influenced by physicochemical properties and ionic strength of the solution. Ionic strength and pH are the most important factors and their effects on flow behaviour of gums have been investigated in many studies. The objective of this study was to investigate the effect of the simultaneous changes of pH and calcium salt on rheological behavior of xanthan- gellan gum blends. Materials and Methods: The salt (CaCl2, 1 and 5mM) was added to gum solutions after adjusting pH values (3, 5 and 7) and rheological measurements were carried out using Brookfield rheometer (LV DV III) at 25 ˚C. Rheological behaviour of gum solutions were adjusted to Herschel–Bulkley model and the effect of the factors on rheological parameters were determined. Results: Findings showed that pH variations affect the interaction between gum and calcium cations. Adding salt, reduced slightly the apparent viscosity of mixtures with low pH values (pH=3). Gums structures, mixing ratio and salt concentration had important effects on rheological behavior of the mixtures. Conclusion: Results showed that pH variations and salt concentration affect the rheological behavior of xanthan- gellan gum blends. So the desired function of the gums in the foods is influenced by pH and ionic strength of the food matrix and investigating the effect of other salts and acids is recommended. Keywords: Xanthan gum, Gellan gum, Steady shear rheology, Calcium salt