Optical enhancement and control of the nonlinear optical (NLO) properties of organic compounds can be expected at the excited state because of changes in dipole moments and oscillator strength caused by electron density distribution different from that at the ground state. We constructed a novel measurement system of hyperpolarizability β at the excited state of molecules in solutions. The system was based on nanosecond Hyper-Rayleigh Scattering (HRS) method with CW laser excitation. In the HRS technique, a chromophore solution was irradiated by YAG laser beam of various intensities (frequency ω), and the scattered photons at 2ω were detected. The HRS intensity was proportional to the square of the incident laser intensity. The increase of HRS intensity forp-nitroaniline was observed in methanol solutions upon excitation with CW Ar laser at 457.9 nm. The β-value at the excited state was estimated.