Abstract.Optical Second-Harmonic Generation (SHG) in reflection from a polycrystalline copper surface in air was studied using femtosecond time-resolved pump and probe measurements at =625nm. The observed time dependence of second-harmonic yield from the probe beam demonstrates, that SHG is a very sensitive technique for measuring transient electron temperatures of metals even when these are covered by an oxide layer. For polycrystalline copper, an electronphonon energy transfer time of 2ps was observed, corresponding to a coupling constant of 3.751017W/m3K at average lattice temperatures of about 500K. The analysis of experimental data indicates that the time dependence of SHG is governed by the linear dielectric function which, in turn, is affected by the electron temperature. There is no evidence for a temperature dependence of the nonlinear susceptibility (2) .