The rheological and filtration properties of drilling mud under down-hole conditions may be very different from those measured at ambient pressures and temperatures at the surface. This paper presents the results of an experimental investigation into the temperature and salinity and pH effects on drilling mud rheological and filtration properties. Results are given from tests on water base mud containing CMC Polymer and XC Polymer. Drilling fluid was investigated at three different temperatures (21.1°C, 48.9°C, 80°C) containing 8.165Kg/bbl bentonite. The drilling mud salinities in this study were fresh water (Ahwaz water: ppm: 400, Hardness: 120), 2000 ppm, 4000 ppm, 8000 ppm and 40000 ppm. It was found that pH of drilling mud should be kept at range of 8-10, because increasing pH of drilling mud will increase its rheological properties. The salinity and temperature effects show that as the salinity and temperature of drilling mud are increased the effectiveness of Polymers in drilling mud will decreased. Moreover, they have a negative effect on filtration properties of drilling mud. In suspensions of sodium montmorillonite that are well dispersed and have low gel strength, both plastic viscosity and yield point decrease with increasing temperature.