In this work we analyze the star formation rates and stellar masses of a sample of 157 star forming galaxies at z ˜ 0.84 (Villar et al. 2008), selected by their Hα flux with a narrow band filter. We compare star formation rates (SFR) measured with different tracers (Hα, UV and IR) finding that they are in good agreement after extinction correction, although with some scatter. We find a correlation between the ratios SFR_{FUV}/SFR_{Hα}, SFR_{IR}/SFR_{Hα} and the EW(Hα) (i.e. weighted age) which accounts for part of this scatter. We obtained stellar mass estimations fitting templates to multi-wavelength photometry. The typical stellar mass of a galaxy within our sample is ˜ 2 x 10^{10} M_&sun;. The specific star formation rate (sSFR) decreases with it, indicating that massive galaxies are less affected by star formation processes than less massive ones. In addition, the sSFR is, for a fixed mass, higher in the Universe at z˜ 0.84 than in the local one. Both results are consistent with the downsizing scenario. To quantify this downsizing we estimated the quenching masses for our sample at z ˜ 0.84 and a local sample also selected by Hα, finding that it declines from M_Q ˜ 10^{12} M_&sun; at z ˜ 0.84 to M_Q ˜ 8 x 10^{10} M_&sun; at the local Universe.