The interactions between negatively charged diblock polyelectrolyte PDMA(71)-b-PAA(59) and oppositely charged gemini surfactant hexylene-1,6-bis(dodecyldimethylammonium bromide) (12-6-12) in basic media were studied using dynamic light scattering, fluorescence spectroscopy, surface tension, and (1)H NMR. With increased addition of surfactant, the conformation of polyelectrolyte experienced changes from the initial unimer with open-extended PAA block, to the nano-scaled aggregates/complexes with a maximum hydrodynamic diameter (D(h)), and finally to the stable complexes with a smaller D(h). Accordingly, the value of D(h) during the whole process of increasing the surfactant concentration changed from 14-17 nm, to 184 nm, and to the final 70 nm, respectively. This transformation was driven by the electrostatic attractive/repulsive interactions, the hydrophobic interaction between hydrophobic surfactant tails, and the hydrophilicity of PDMA block.