The effect of conductor surface roughness on electro-thermally (ET) induced passive intermodulation (PIM) products is analysed and discussed. The analytical model combined with the commercial simulator SIMBEOR is used to examine the products of ET nonlinearity, which is significantly influenced by the surface topography of the conductor. It is further shown that, in spite of the rise of ohmic losses with frequency, conductor roughness may somewhat allay the ET-PIM growth due to concurrent increase of additional heat-sinking provided by the interiors of dendrites and conductor cladding.