Diffusion coefficients (D) of unstable transient radicals are measured by the transient grating setup with a high wavenumber in a timescale from 100 ns to a few microseconds. D of the radicals created by the hydrogen-abstraction reaction determined in this timescale are the same as those determined previously in a longer time region of 100 mu s to similar to 10 ms. This result confirms that D of the initially created hydrogen-abstracted radicals are smaller than those of the parent molecules with similar shapes and sizes. D of the 4-aminophenylthiyl radical, which recombines with a lifetime of similar to 50 mu s is measured for the first time. It is found that D of this radical is similar to that of p-chloroaniline, which is an analogous closed-shell molecule.