Transparent, nonlinear Bis(L-threonine) copper (II) monohydrate [BLTCM], the semiorganic optical crystal was synthesized by a conventional slow evaporation solution growth technique. The synthesized crystals were investigated to reveals its excellent performance. The third order nonlinear optical properties of BLTCM sample in WATER was measured by the Z-scan technique using 532nm diode pumped solid state laser. This material exhibits negative optical nonlinearity. The sample at around 62 % transmittance exhibited non-linear refractive coefficient of the order of 10-9 (cm2/W), nonlinear absorption coefficient of the order of 10-4 cm/W and nonlinear susceptibility of the order of 10-6 esu. These results show that BLTCM sample has potential applications in nonlinear optics.