The influence of Mn-doping on the nonlinear optical (NLO) properties and crystalline perfection of tris(thiourea)zinc(II) sulphate (ZTS) single crystals grown at 30 degrees C by slow evaporation Solution growth technique (SEST) has been investigated. Incorporation of Mn-dopant into the crystal lattice even at the low concentrations was well confirmed by energy dispersive X-ray spectroscopy (EDS). Powder XRD and FT-IR analyses confirm the slight distortion in the structure of the crystal at high concentrations of dopants. Close observation of powder XRD of pure and doped specimens reveals some interesting features in the XRD profiles with changes in intensity and position of some peaks due to stress developed in the crystal because of doping. A nominal increase in cell parameter values is also observed. High-resolution X-ray diffraction (HRXRD) studies reveal many interesting aspects of the effect of dopants on crystalline perfection which in turn shows a good correlation with second harmonic generation (SHG) efficiency. The present investigation shows that the full width at half maximum (FWHM) of the diffraction curves (DC) increased with the dopant concentration. However, at the higher concentrations of the dopants (> 10 mol%), the DCs exhibit additional peaks due to the formation of structural grain boundaries. The SHG efficiency is enhanced greatly when the concentration of dopants is low and no significant enhancement is observed at high concentrations due to deterioration of the crystalline perfection. (c) 2008 Elsevier B.V. All rights reserved.