We analyze the one loop corrections to leptonic W and Z decays in an R-parity violating extension to the minimal supersymmetric standard model. We find that lepton universality violation in the Z line-shape variables alone would strengthen the bounds on the magnitudes of the lambda' couplings, but a global fit on all data leaves the bounds virtually unchanged at \lambda'(33k)\less than or equal to 0.42 and \lambda'(23k)\less than or equal to 0.50 at the 2 sigma level. Bounds from W decays are less stringent: \lambda'(33k)\less than or equal to 2.4 at 2 sigma, as a consequence of the weaker Fermilab experimental bounds on lepton universality violation in W decays. We also point out the potential of constraining R-parity violating couplings from the measurement of the Y invisible width.