  In this talk I report my recent study on the shear viscosity of neutron-rich
nuclear matter from a relaxation time approach. An isospin- and
momentum-dependent interaction is used in the study. Effects of density,
temperature, and isospin asymmetry of nuclear matter on its shear viscosity
have been discussed. Similar to the symmetry energy, the symmetry shear
viscosity is defined and its density and temperature dependence are studied.
