Using Rivlin and Erickson constitutive equation, the rotational instability of a second order fluid contained between two concentric rotating cylinders has been examined. It is found that the marginal instability is governed by a sixth order eigen value problem. The critical Taylor's number which determines the onset of instability has been determined as a function of m (=Ω2/Ω1), a (wave length) and S (=2S1+S2), with the help of a modified Galerkin technique. Figures 1 to 4 show the effect of second order terms on Taylor's number, radial velocity and streamlines.