The deuterium isotope effect on the solvation dynamics and the anisotropy decay of coumarin 480 (C480) in a room temperature ionic liquid (RTIL) microemulsion is studied by femtosecond up-conversion. The microemulsion consists of the RTIL 1-penty1-3-methyl-imidazolium tetra-fluoroborate ([pmim][BF4]) in triton X-100 (TX-100)/benzene. Replacement of H2O by D2O in the microemulsion causes retardation of solvation dynamics. The average solvation time of C480 () in RTIL microemulsion with 5 wt % D2O is similar to 1.5-1.7 times slower compared to that in the H2O containing RTIL microemulsion. This suggests that the main species in the microemulsion responsible for solvation is the water molecules. In both D2O and H2O containing RTIL microemulsion, the solvation dynamics exhibits marked dependence on the excitation wavelength (lambda(ex)) and becomes about 15 times faster as lambda(ex) increases from 375 to 435 nm. This is ascribed to the structural heterogeneity in the RTIL microemulsion. For lambda(ex) = 375 nm, the region near the TX-100 surfactant is probed where bound water molecules cause slow solvation dynamics. At 435 nm, the RTIL pool is selected where the water molecules are more mobile and hence gives rise to faster solvation. The average time constant of anisotropy decay shows opposite dependence on lambda(ex) and increases about 2.5-fold from 180 ps at lambda(ex) = 375 nm to 500 ps at lambda(ex) = 435 nm for D2O containing RTIL microemulsion. The slower anisotropy decay lambda(ex) = 435 nm is ascribed to the higher viscosity of RTIL which causes greater friction at the core.