The aggregation behavior of cationic gemini surfactants with respect to variation in head group polarity and spacer length is studied through conductance, surface tension, viscosity, and small-angle neutron-scattering (SANS) measurements. The critical micellar concentration (cmc), average degree of micelle ionization ( β ave ), minimum area per molecule of surfactant at the air–water interface ( A min ), surface excess concentration ( Γ max ), and Gibb's free energy of micellization ( Δ G mic ) of the surfactants were determined from conductance and surface tension data. The aggregation numbers ( N), dimensions of micelles ( b / a ), effective fractional charge per monomer ( α), and hydration of micelles ( h E ) were determined from SANS and viscosity data, respectively. The increasing head group polarity of gemini surfactant with spacer chain length of 4 methylene units promotes micellar growth, leading to a decrease in cmc, β ave , and Δ G mic and an increase in N and b / a . This is well supported by the observed increase in hydration ( h E ) of micelles with increase in aggregation number ( N) and dimension ( b / a ) of micelle.