Association behavior of poly(N,N-dimethylacrylamide)-graft-poly(methyl methacrylate) in dilute solution of mixed solvent of methanol/water has been investigated by using light scattering, where association strength of grafted chains is controlled by changing the water content. The following points are demonstrated: (1) the increase in water content in solvent starting from pure methanol increases the association strength, resulting in the formation of inter-molecular associations at water contents higher than 20-30 wt% of water, (2) the association number, N-a, depends on the changing rate of water content of solvent, At higher changing rates, associates of small N-a ( = 2-4) are formed by the dominance of intra-molecular association, while the slower change of water content yields larger associates of N-a being of the order of 10. The presence of the optimum changing rate of solvent quality for inter-molecular associations is suggested. This process dependence of associate structure is discussed on the basis of association kinetics.