Mono-carboxy terminated polystyrene oligomer (MCPS) and di-carboxy terminated polystyrene oligomer (DCPS) were prepared by anionic polymerization. Viscometry and dynamic light scattering (DLS) studies show that both MCPS and DCPS can interact with poly(4-vinyl pyridine) (PVPy) via hydrogen bonding to form soluble graft-like complexes in CHCl3. The marked differences in the viscosity-composition behaviour, intrinsic viscosities and hydrodynamic radius distribution f(R-h) between MCPS/PVPy and DCPS/PVPy blend solutions proved that the two carboxyl ends in DCPS provide much stronger ability for complex formation than the mono carboxyl end in MCPS does.