Measurements of Z to Heavy-quark couplings at SLD

We present measurements of Z to heavy-quark coupling electroweak parameters, Rb, Rc, and parity-violation parameter Ac, from SLD. The measurements are based on approximately 550k hadronic Z events collected in 1993-98. Obtained preliminary results of Rb and Rc measurements are Rb = 0:2159 0:0014 0:0014 and Rc = 0:1685 0:0047 0:0043. In the Ac measurement, we use four methods to determine the initial-quark charge: combined Kaon charge and Vertex charge, lepton, exclusively reconstructed D*, D-mesons, and a new method using inclusive soft-pion from D*. The preliminary results of these four methods were combined to give Ac = 0:634 0:027.