Nonlinear equations of motions of a rotating ellipsoid of viscous uniform gas are derived. The problem is made tractable by introducing a somewhat special but reasonable formula for the viscosity of the gas, and the general behavior of the ellipsoid is discussed. Once the ellipsoid is deformed as a > a, > a, (say), where a1, a,, and a, designate the lengths of the semiaxes of the ellipsoid, its subsequent figures remain so until the oscillation is damped completely. In finite-amplitude oscillations, the viscous stresses prevent the ellipsoid from becoming elongated rapidly. The total circulation of gas does not always decay monotonically, but grows depending on the configuration of the ellipsoid. Perturbations of the toroidal modes are applied to axisymmetric ellipsoids initially, and numerical integrations of the nonlinear equations are carried out Growing oscillations and secular deformations of the Maclaurin spheroid beyond the classical point of bifurcation are demonstrated. Dynamical evolution and rapid gravitational collapse of gaseous ellipsoids in free precession are also followed numerically. The large-amplitude oscillations after the first bounce amplify an initially small precession, performing upside-down motions of the ellipsoidal figure.