Compatibility was investigated for blends of one-end-aminated polystyrene (APS) and one-end-sulfonated poly(ethylene glycol) (SPEG) in toluene with changing the association strength and the segment interaction by varying the total polymer concentration. Weight-average molecular weight of APS and SPEG were 5600 and 5700, respectively. Cloud-point concentrations at fixed temperature were measured as a function of the polymer composition. It was demonstrated that the association strength between the amino and sulfonic end groups was strong enough to give two peaks to the misibility gap in the space of solvent volume fraction against the polymer composition, which was theoretically expected for a strong-association system. It was also found that sulfonic groups introduced to PEG chain ends reduced the miscibility of PS and PEG due to association between the sulfonated ends. A Flory-Huggins type theory of associated polymer blend solution could interpret these experimental results qualitatively.