K2Ti6O13 whisker was synthesized by the calcination and slow-cooling method, and the microstructural evolution of whiskers, and the relations between the phase and the layer structure, were investigated. The amount of K2O in the starting powder mixture played a key role in forming a layer structure, which can be obtained by addition of excess K2O. During calcination, rod-like K2Ti6O13 particles with a layer structure were formed by reactions between K2O and TiO2. During slow-cooling, the K2O-rich liquid phase reacted with K2Ti6O13 layers near the boundary and K2Ti4O9 whiskers were produced by the splitting of layers within rod-like K2Ti6O13 particles. K2Ti4O9 whiskers were reformed into K2Ti6O13 whiskers by treatment in boiling water and reheating. The synthesized K2Ti6O13 whiskers had a clean surface and a length exceeding 100 mu m.