  We present measurements of the branching fraction and CP-violating
asymmetries in the decay $B^0 \to f_0(980)K^0_S$. The results are obtained from
a data sample of $123\times10^6$ $\Upsilon(4S) \to B\bar{B}$ decays. From a
time-dependent maximum likelihood fit we measure the branching fraction ${\cal
B}(\Bz\to f_0(980)(\to\pi^+\pi^-)K^0)=(6.0\pm0.9\pm0.6\pm1.2)\times 10^{-6}$,
the mixing-induced CP violation parameter $S=-1.62^{+0.56}_{-0.51} \pm 0.09\pm
0.04$ and the direct CP violation parameter $C=0.27\pm 0.36\pm 0.10 \pm 0.07 $,
where the first errors are statistical, the second systematic and the third due
to model uncertainties. We measure the $f_0(980)$ mass and width to be
$m_{f_0(980)}=(980.6 \pm 4.1 \pm 0.5\pm 4.0){\rm MeV}/c^2$ and
$\Gamma_{f_0(980)}=(43^{+12}_{-9} \pm 3 \pm 9){\rm MeV}/c^2$, respectively.
