Single crystals Of L-arginine tetrafluoroborate (L-AFB), a semi-organic NLO material, have been grown from aqueous solution. Since L-AFB is known to form highly viscous solution in water, growth by slow cooling has been difficult for optical quality crystals. In this study, highly transparent L-AFB crystals have been successfully grown by slow evaporation by keeping the saturated solution under special condition. The grown crystals were subjected to structural, optical and mechanical property studies. XRD studies reveal that L-AFB crystals possess orthorhombic structure. Fourier transform infrared absorption studies confirm the chemical constituents and presence of functional groups in the grown crystals. L-AFB crystals possess a higher hardness values compared to other semi-organic crystals. The linear and nonlinear optical properties of the grown crystals have also been studied. (C) 2002 Elsevier Science B.V. All rights reserved.