The interaction of poly(N-vinylformamide) (PNVF) with anionic surfactant, sodium dodecyl sulfate (SDS), has been studied by pyrene fluorescence and two-dimensional nuclear Overhauser effect spectroscopy (21) NOESY). With use of pyrene as the probe, from low to high concentration of SDS, the pyrene I-1/I-3 plot exhibits three stages of association of PNVF with SDS. The I-1/I-3 plot vs [SDS] shows a well-defined plateau (I-1/I-3 = 1.47) at SDS concentrations ranging between 3 and 10 mM, indicating that in this range of SDS concentrations the sizes of polymer-bound SDS aggregates are approximately identical. The ambiguity in determining the critical aggregation concentration (cac) of SDS from the I-1/I-3 plot vs [SDS], which resembles the typical profile of surface tension vs surfactant concentration, has been clarified by the 2D NOESY experiment. Also, just beyond the cac ([SDS] = 3 mM), definite proof of formation of the PNVF-SDS complex bound on the polymer chain is provided by the 2D NOESY experiments. On the basis of the inter- and intramolecular cross-relaxation between the protons of PNVF and SDS, the microstructure of PNVF-induced SDS aggregates is proposed. Moreover, the association behavior of PNVF with SDS is compared to that of the poly(vinylpyrrolidone) (PVP)/SDS and poly(ethylene oxide) (PEO)/SDS systems.