The rheological properties of polybutadiene(PB)/polyisoprene(PI)in the unstable and metastable regions under oscillatory shear flow has been studied.Based on the shear quench experiment,it showed that the time dependent storage modulus G initially increased and then decreased with time in the unstable region.The concentration fluctuation led to the increasing part and the coarsening of the bicontinuous structure led to the decreasing of the storage modulus.The rheological response of the nucleation/growth in the metastable region was similar to that of spinodal decomposition.The fluctuation-assisted nucleation theory proposed by Balsara et al was similar to the spinodal decomposition mechanism,which led to the similar rheological response.However,the continuous nucleation led to the slow growth and the almost linear decayed rheological curve,which was different from that in the unstable region.Moreover,the relative nucleation rate on the early stage of nucleation was also calculated by this theory,which increased exponentially with the reciprocal of quench temperature in the metastable region.