Potassium niobate crystals have been synthesized by a molten salt process with KCl, K2SO4, K2CO3 or KNO3 as molten salt reactive Nb2O5 materials at 900 ℃ for 2 h. The effect of different kinds of molten salt on the structure and morphological profile of the powers were discussed, and the optical properties of the samples were studied. X-ray diffraction results showed that the product is KNb3O8 when the KCl and K2SO4 as molten salt, respectively, and the product is K2NbO4 when the K2CO3 and KNO3 as molten salt, respectively. Scanning electron microscopy results showed that bar was formed with the width of 0.2~0.5 μm and the length of several microns. Using K2SO4 as molten salt, the width of rod is 0.2~1 μm and the length is 1~25 μm. Using K2CO3 as molten salt, the product is not rod-like structure, but irregular granular structure. Using KNO3 as molten salt, the width of rod is 0.2~1 μm and the length is 0.5~4 μm. Part of the rod-like structure connected together. Fluorescence spectra showed that KNb3O8 and K3NbO4 crystals have good fluorescence. Fluorescence studies have shown that the samples have very similar fluorescence spectra with K2SO4, KNO3 and K2CO3 as the molten salt. The samples have good fluorescence which were prepared using KCl, K2SO4 and K2CO3 as molten salt.