Measurements of the real σ1 and imaginary σ2 part of the conductivity were performed in optimally doped BaFe1.9Ni0.1As2 and overdoped BaFe1.88Ni0.12As2 crystals in the frequency range 20MHz–1.5GHz using a single coil technique. The temperature dependence of the London penetration depth follows a T2 law. The conductivity σ1 increases with decreasing temperature below Tc in agreement with the results obtained for the optimally Co doped BaFe2−xCoxAs2 crystals. The increase of σ1 in the superconducting state is attributed to a rapidly decrease of the quasiparticle scattering rate. •Surface impedance measurements on superconducting BaFe2−xNixAs2 crystals are reported.•Real part of the conductivity increases below the superconducting transition.•Determination of the quasiparticle scattering time.