Hyper-Rayleigh scattering (HRS) technique is used to study the nonlinear optical response of nanocrystalline gold particle suspensions. The signal intensity measured at 400 nm has a cubic dependence on the pump laser energy at 1064 nm, indicating that the measured signal is due to a third-order nonlinear optical process, namely three-photon excited fluorescence (3PF). To the best of our knowledge, this is the first experimental observation of 3PF for colloidal gold nanoparticle suspensions.