Single crystals of YCa9(V1−xNbxO4)7 were grown using the Czochralski method. Their structure and the second-harmonic generation (SHG) were investigated. Structural refinements of these crystals show that when x is equal to 0.04, the {VO4} tetrahedra are most distorted. The SHG measurements reveal that the SHG intensity increases with increasing the Nb concentration until the formation of Y3NbO7 phase, and the optimum concentration of Nb substituting for V in the crystal is 4 mol%, which provides the maximal SHG efficiency and allows the realization of phase-matching for a Nd:YAG 1.064 μm laser. Nb doping makes YCa9(V1−xNbxO4)7 crystals potential for nonlinear optical applications.