The crystal growth experiment of Nb : KTP crystal has been reported. The effect of Nb concentration and seed crystal on the Nb : KTP crystal growth has also been studied. The type II phase-matched (PM) second harmonic generation (SHG) cut-off wavelength and optimal SHG PM angle of Nd : YAG 1.0642 mu m laser and Nd : YAlO3 1.0795 mu m laser have been measured. It shows that Nb concentration has a great effect on both crystal growth and nonlinear optical properties. On the one hand, Nb ion produces new problem in crystal growth; on the other hand, it improves the nonlinear optical properties and widens the application of KTP crystal. The X-ray powder diffraction data of 7.5 mol% Nb : KTP are also presented. It shows that the crystal structure of Nb : KTP has some changes when Nb dopes into the crystal, but the change is small.