A new approach for the synthesis of K4Nb6O17.3H(2)O by hydrothermal method was examined using different alkaline solutions such as Nb2O5-KOH-NaOH-H2O, Nb2O5-KOH-NH4OH-H2O and Nb2O5-KOH-H2O. K4Nb6O17.3H(2)O was formed as single phase in Nb2O5-KOH-H2O system in the region of KOH concentration 1.0-1.5 m and temperature 220-285 degrees C. KNbO3 was also formed as single phase in 3.0 m KOH solutions above 250 degrees C. Addition of methanol was useful to decrease the particle size and increase the specific surface area of K4Nb6O17.3H(2)O