Single crystals of KNd(PO3)(4) (KNP) and KGd(PO3)(4) (KGP) with P2(1) space group have been successfully grown by the top seeded solution growth technique from the high-temperature self-flux melts. The as-grown crystals were transparent with sizes of 14 x 28 x 20 mm(3) (KNP) and 13 x 36 x 19 mm(3) (KGP). The X-ray diffraction, infrared spectra, transmittance spectra and specific heat capacity of title compounds have been determined. Finally, we measured the second harmonic generation efficiencies while KH2PO4 (KDP) as reference sample, and discussed the differences of the efficiencies of the powders and the single crystals induced by preferred orientation and self-absorption of Nd3+. (C) 2010 Elsevier B.V. All rights reserved.