  We discuss the shear viscosity of the quark matter by using the Kubo-Mori
formula. It is found that the shear viscosity is expressed in terms of the
quark spectral function. If the spectral function is approximated by a modified
Bright-Wigner type, the viscosity decreases as the width of the spectral
function increases. We also discuss dependence of the shear viscosity on the
temperature and the density.
