Transparent single crystal of bis guanidinium hydrogen phosphate monohydrate of length 45 mm and diameter 16 mm have been grown from saturated solution of deionized water adopting Sankaranarayanan-Ramasamy method. Optical properties such as its transmittance, band gap, Phase-matching angle, spectral phase matching bandwidth were measured and their values are compared with the standard compounds. Third order nonlinear optical property was found using Z-scan technique. Optical limiting property of the title material has also been discussed. © 2016