In this study, we investigated the effect of the polymer molecular weight on the cooperative complexation of alpha-cyclodextrin (alpha-CD) with alternating copolymers of sodium maleate and dodecyl vinyl ether (pC(12)M) by H-1 NMR measurements. It was confirmed that the pC(12)M prepared formed micelle-like aggregates in aqueous media by steady state fluorescence and sedimentation equilibrium experiments. Using the NMR data, the concentrations of free and complexed alpha-CD (C-CD,C-f and C-CD,C-c, respectively) were calculated and the CCD, values were plotted as a function of C-CD,C-f to prepare binding isotherms. The binding isotherms exhibited sigmoidal curves for all the polymers examined, indicative of cooperative complexation. The binding isotherms also indicated that the complexation was more cooperative for pC(12)M of a higher molecular weight. Analysis of the binding isotherms using a model proposed based on the one-dimensional lattice theory indicated that the molecular weight dependency of the cooperative complexation was due to molecular dependent attractive interactions between free dodecyl groups and between complexed alpha-CD molecules.