In transforming $K_2Ti_4O_9$ whisker, synthesized by calcination and slow cooling method, into $K_2Ti_6O_{13}$ whisker with boiling water and hydrochrolic acid, the effect of their treatment time and concentration on phase transformation, surface state and scattering of whisker was examined. The result was that the surface state of whisker was improved and whisker with a small diameter and a considerable aspect ratio was obtained by inducing scattering of a bundle of whisker. The treatment by boiling water and hydrochrolic acid induced the phase transformation of $K_2Ti_4O_9$ into $K_2Ti_6O_{13}$ and the phase transformation proceeded by extration of $K^+$ ion.