Mixed crystals of two nonlinear optical materials, L-arginine hydrochloride monohydrate (LAHCl) and L-arginine hydrobromide monohydrate (LAHBr) have been grown from aqueous solution by slow evaporation at constant temperature (28degreesC) and also by slow-cooling method (0.5degreesC/day). The mixed crystal belongs to the monoclinic system with space group P2(1) and lattice parameters a = 11.158(2) Angstrom, b = 8.579(3) Angstrom, c = 11.235(3) Angstrom, beta = 91.55degrees(4). The mixed crystal is transparent down to 240nm and its second harmonic generation efficiency for 1064nm laser radiation is almost the same as that of parent crystals LAHCl and LAHBr. Whereas the damage threshold of the mixed crystal is higher than that of LAHBr but nearer to LAHCl. (C) 2002 Elsevier Science BN. All rights reserved.