The highly stable colloidal structure of graphene oxide (GO) in aqueous dispersion behaves as a platform for the molecular aggregation of dyes via a simple adsorption process. The interaction between dye and GO sheets is a critical factor for dye aggregation. Positively charged dyes interact with the negatively charged GO sheets in an aqueous dispersion via both electrostatic and π–π stacking interactions. The cationic nature of Pyronin Y (PyY) ensures that the dye molecules are quickly adsorbed on the GO sheets in the aqueous dispersion. GO–PyY composites with different ratios, which are stable for months, are prepared by simply mixing diluted aqueous dispersions of both components. Transition dipole–dipole interactions between the adsorbed dye molecules on the surface of the GO sheet causes the formation of H-aggregates of the dye at dilute concentrations. H-aggregates of PyY are characterized by spectroscopic techniques (UV-Vis, steady-state and time-resolved fluorescence spectroscopy). The morphology and thickness of the GO sheets and the dye adsorbed GO sheets were determined using atomic force microscopy (AFM) in tapping mode. AFM studies revealed that a great deal of PyY molecules interact on the edges of the GO sheets.