Based on the established theory of photoinduced exciton bleaching of the polymers with nondegenerated ground state,we calculated the transient mirrorless optical bistability of photoexcitation and relaxation processes in the polymers.The results show that the transient saturation absorption mirrorless optical bistabilities and the increasing absorption mirrorless optical bistabilities can be obtained from the ultrafast excitation and relaxation processes in the polymers with nondegenerate ground state,and the switching time of the optical bistabilities is of the order of fs or ps.With the increase of the delay time of the probe pulse relative to pump pulse,the nature of mirrorless optical bistability can change from the saturation absorption optical bistability to increasing absorption optical bistability,and the rate of change is proportional to the speed of relaxation of the photoinduced exciton.