  We present measurements of $Z^0$ to heavy-quark coupling electroweak
parameters, $R_b$, $R_c$, and parity-violation parameter $A_c$, from SLD. The
measurements are based on approximately 550k hadronic $Z^0$ events collected in
1993-98. Obtained preliminary results of $R_b$ and $R_c$ measurements are $R_b
= 0.2159 \pm 0.0014 \pm 0.0014$ and $R_c = 0.1685 \pm 0.0047 \pm 0.0043$. In
the $A_c$ 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 $A_c =
0.634 \pm 0.027$.
