The effect of ammonium malate on the growth rate, structural, optical, thermal, mechanical, dielectric properties, crystalline perfection and second harmonic generation (SHG) efficiency of ammonium dihydrogen phosphate single crystals grown by the slow cooling method has been investigated. The lattice parameters of the grown crystals were obtained by the single-crystal X-ray diffraction analysis. Fourier transform infrared studies confirm the functional groups of the crystals. UV-vis study shows that the transparency is increased much by the dopant. Thermal analysis was performed to study the thermal stability of the grown crystals. Vickers hardness measurements reveal the higher hardness of the doped crystals. Low dielectric losses were observed from the dielectric measurements for the doped ADP crystals. The high-resolution X-ray diffraction studies show that the crystalline perfection of the crystals is good. The relative SHC efficiency measurements revealed that the dopant has enhanced the efficiency. (C) 2009 Elsevier B.V. All rights reserved