Organic nonlinear optical crystals have several advantages over inorganic crystals for frequency conversion and electro-optic modulation. In the present work, the effect of 100 MeVAg14+ion irradiation on the electrical and optical properties of organic nonlinear crystal para-hydroxy acetophenone (HAP) is investigated. It is observed that second harmonic generation efficiency is marginally affected. However, changes in refractive index and dielectric constants (13 times higher) are noticed in the irradiated HAP. ©1997 American Institute of Physics.