Flux-Flow and Fluctuations in the Microwave Resistivity of <font>YBa</font>2<font>Cu</font>3<font>O</font>7-δ

We present measurements of the microwave resistivity at 48 GHz in YBa 2 Cu 3 O 7-δ film, as a function of the temperature and the magnetic field. The magneto-dissipation from 60 K up to a few kelvins below Tc finds a quantitative description in terms of free flux flow. Approaching Tc, the data are not consistent with a dissipative mechanism based solely on flux dynamic. Fluxon viscosity is measured as a function of the temperature, and the in-plane coherence length is estimated. The analysis of the zero-field transition at 48 GHz in terms of anisotropic renormalized fluctuations yields identical estimate.