NaClO3 and NaBrO3 are believed to form a complete solid solution from RT to fusion. The unique solid phase can thus be written: NaClO3 (1-x)-NaBrO3 (x) with: 0 ≤ x ≤ 1. This study shows that at high temperature this statement might be valid. Nevertheless, up to 50°C and probably up to 160°C and even higher temperature, this is not true when the system is in thermodynamic equilibrium. A large miscibility gap exists at room temperature (RT). This gap could be reduced up to a complete disappearance by fast crystallization, for instance by spray-drying. The necessary conditions to access to equilibrium including homochirality are also discussed.