Platelet KNbO₃ particles having perovskite single phase have been successfully synthesized by a new simple procedure based on the dry-mixing technique and self-flux method using KNO₃ source that required no washing and filtration process. Well-crystalline edge-shaped platelet KNb₃O₈ particles were first obtained by the reaction between KNO₃ and Nb₂O₅. Next, they were reacted with second KNO₃ to form platelet KNbO₃ particles by the topochemical conversion method. The platelet KNbO₃ particles synthesized at 800°C demonstrated a relatively high aspect ratio of around 5 with edge lengths of about 2–10 and 10–40 µm in size for the tabular and thickness directions, respectively. The topochemical conversion mechanism from KNb₃O₈ to KNbO₃ was also proposed in this study.