A semiorganic nonlinear optical crystal, L-arginine hydrochloride monohydrate (LAHCM), was grown successfully by slow evaporation using deionized water over 45 days. Single crystal XRD confirmed the monoclinic crystal system with space group P21. Optical, mechanical, thermal, and surface properties were analyzed using Kurtz-Perry, Z-scan, microhardness, TGA/DTA, and etching techniques. The SHG efficiency of LAHCM was 1.077 times greater than KDP. Nonlinear optical parameters measured by Z-scan include refractive index n2 = 1.06 × 10^-15 m²/W, absorption coefficient β = 2.424 × 10^-10 m/W, and third-order susceptibility χ(3) = 4.788 × 10^-14 esu. Thermal stability was 121 °C. Microhardness study confirmed LAHCM as a hard material, and surface etching revealed time-dependent surface characteristics. © 2023 Elsevier B.V., All rights reserved.