Abstract Phase equilibrium and dielectric characterisation of the binary system SrNb 2O 6-NaNbO 3 were investigated through DTA, crystallographic, Curie point, and hysteresis loop measurements. Similarly to previous results on alkaline-alkaline earth niobates, ferroelectric solid solutions with the tungsten bronze structure are stable at room temperature between 69 and 79 mol.% SrNb 2O 6. In the 65–69 % range a tungsten bronze phase occurs at high temperature. On the other hand, a new compound with cubic symmetry at room temperature is determined for 33 mol.% SrNb 2O 6, which undergoes a phase transition at − 100°C into a ferroelectric state. The solubility range of this compound extends to 14 mol.% SrNb 2O 6. Between 14 and 33 % ferroelectric solid solutions have a slightly distorted cubic symmetry below their Curie temperature, which is found-to vary from − 100°C to + 200°C. Finally it has been shown that small amounts of SrNb 2O 6 incorporated in NaNbO 3 (2,5 mol.% SrNb 2O 6) drive ferroelectric the room temperature antiferroelectric phase of NaNbO 3.