The effects of the chain length, active end group and concentration on the association of living polystyryllithium (PS-Li+) chains in benzene were examined by a combination of static and dynamic laser light scattering in a cuvette equipped with a high-vacuum stopcock. The results show that long PS-Li+ chains (Mw 1 × 104) usually form dimers in the solution. In contrast, shorter PS-Li+ chains exhibit two relaxation modes, where the fast mode is related to the translational diffusion of the living chain dimers. The end capping of the living chain with bulky 1,1-diphenylethene (DPE) leads to an intensity increase of the slow mode, indicating that the slow mode is not due to the chain aggregates but to temporal aggregates or long-range density fluctuation induced by weak electrostatic dipole-dipole interaction between ionic pairs at the chain ends.