We have investigated the effect of protic ionic liquid, N,N-Dimethylethanolammonium formate (DAF) addition on Triton X-100-cetyltrimethylammonium bromide (CTAB) mixed micellar solution. We have shown the effect of DAF addition on the size and zeta potential of the mixed micellar aggregates using dynamic light scattering measurements. The steady-state and time-resolved fluorescence spectroscopy have been used to investigate the effect of increasing CTAB/Triton X-100 ratio and DAF addition on the solvent and rotational relaxation of Coumarin-153 in CTAB-Triton X-100 mixed micellar solutions. The average solvation time decreases with increasing CTAB/Triton X-100 ratio and increases with the addition of DAF. (C) 2012 Elsevier B.V. All rights reserved.