Abstract: Water soluble potassium ions in potassium hexatitanate whiskers (PTW) of calcination synthesis were investigated in this paper.Experiments showed that the dissolved potassium ions were stripped slowly and not derived from the crystal structure of PTW.With the increase of the concentration of potassium ions the pH value of PTW suspension increased.The analysis based on the experimental results and growth mechanism of PTW showed that there should be trace K₂O between nano-structure gaps on the surfaces of PTW.Thus the trace K₂O between nano-structure gaps led to water soluble potassium ions in PTW.Moreover, potassium ions could be reduced effectively by soaking PTW in dilute acid solution for 8 h or ultrasonic cleaning, and the PTW fit for composites were obtained.The coating of shell (SiO₂) on PTW might hinder dissolution of water soluble potassium ions,but the modification of silanes(A186) on PTW had no influence on the dissolution.