An electrosynthesis in concentrated NaOH electrolyte is first presented for the synthesis of 0.83 mol•L^－1 Na₂FeO₄ solution, and then for the synthesis of solid K₃Na(FeO₄)₂ with high purity and yield. The synthesis conditions have been explored. Many experiment techniques have been used to characterize the obtained solid sample. The experiment results showed that in the mixed NaOH-KOH solutions, the dissolution-precipitation curve of K₃Na(FeO₄)₂ conformed to the empirical foumula of [Na^＋][K^＋]³× [ ]^2.8＝1.4×10^－4 ([K^＋]≤1.01 mol•L^－1). The measured solubility of K₃Na(FeO₄)₂ in concentrated KOH electrolytes was almost the same as that of K₂FeO₄. Different from K₂FeO₄ crystals, the synthesized K₃Na(FeO₄)₂ powders exhibited three characteristic IR absorption peaks (787, 801～802 and 858～862 cm^－1) and a hexagonal unit cell with the space group P m1 (164)．The results of TG/DSC experiments showed that the K₃Na(FeO₄)₂ powders would not decompose until 197 ℃ in the atmosphere of Ar, but were less stable than K₂FeO₄.

Key words: tripotassium sodium ferrate(VI), sodium ferrate(VI), electrosynthesis, IR spectra, XRD, TG/DSC