Nowadays, using GNSS constellations in many applications is clear. The increasing of the satellites availability at any place of the world from different GNSS constellations is compared against using GPS only for improving the positioning accuracy. In this research, the availability of complete GNSS constellations (GPS and GLONASS) at some of IGS stations will be illustrated. Performance with different baseline lengths are assessed using observations from GPS only, GLONASS only and (GPS+GLONASS) using different duration times. The processed data are collected at the same day in two different years. The results approved that using GLONASS only does not give the best accuracy compared to (GPS only and (GPS and GLONASS). Finally the results obtained by the GPS only are close to a large extent with the (GPS and GLONASS) results.