A Raman spectroscopic study has been carried out for aqueous sulfuric acid of various concentrations at room temperature and in the glassy state. Temperature dependence of the Raman spectra was also investigated from 44 to -40 degrees C. Anomalous T-g (glass transition temperature) behavior of the aqueous sulfuric acid solution at similar to 86 wt % H2SO4 is interpreted in terms of ionic species involved in Raman spectral changes. It is shown that ionization of sulfuric acid increases exponentially with decreasing temperature. Complete ionization was attained up to similar to 50 wt % H2SO4 concentration in glassy aqueous H2SO4 solution.