Single crystals of L-histidine hydrochloride monohydrate and tartaric acid mixed L-histidine hydrochloride monohydrate have been grown by slow evaporation solution growth technique from appropriate mixtures of respective chemicals. Single crystal and powder X-ray diffraction analyses, Fourier transform infrared, nuclear magnetic resonance spectral analysis, thermo-gravimetric (TG), differential thermal analysis (DTA) have been employed to characterize the as-grown crystals. It is observed to be a wide transparency window for both the crystals from 300 to 1000 nm, which is suitable for second harmonic generation of laser in the blue region. Nonlinear optical characteristics have been studied using Q switched Nd:YAG laser (lambda=1064 nm). The second harmonic generation conversion efficiency of the grown crystal shows the suitability for frequency conversion applications. (C) 2011 Elsevier B.V. All rights reserved.