Equilibrium phase relations in the Na2O-CaO-SiO2 system at <50 wt% SiO2 concentrations have been experimentally investigated at temperatures between 1200 degrees and 1400 degrees C. The liquidus temperature was determined with differential scanning calorimetry. The equilibrated samples were quenched with high-pressure nitrogen, and examined with electron probe X-ray microanalysis and X-ray diffraction. Based on the experimental results, the liquidus surface projection has been constructed for this temperature range. Six primary phase fields, Ca2SiO4, Ca3Si2O7, CaSiO3, Na2Ca2Si3O9, Na2Ca2Si2O7, and Na2CaSiO4 were identified. The ternary eutectic point of Na2Ca2Si3O9, Na2Ca2Si2O7, and Na2CaSiO4 was determined to be at 1258 degrees C with the composition of 22.5 wt% Na2O, 34.5 wt% CaO, and 43.0 wt% SiO2. The ternary invariant point of the Na2Ca2Si3O9, Na2Ca2Si2O7, and CaSiO3 was established at 1245 degrees C with the composition of 11.8 wt% Na2O, 41.6 wt% CaO, and 46.6 wt% SiO2. The crystalline phase Na2Ca3Si2O8 was also identified in the system.