Electron spin-echo experiments of diphenylnitroxide in benzophenone crystals at low temperatures (48–170 and 4.2 K) are presented. The analysis of two-pulse echo decay at different temperatures indicates that the local field fluctuation in this system is dominated by electron spin-spin relaxation processes. The analysis also implies that the instantaneous spectral diffusion plays an important role in the local field fluctuation in concentrated samples. The spin-lattice relaxation time measurements show that F 1 values are a function of crystal orientation, sample concentration, and temperature. The orientation dependence of T 1 is explained in terms of phonon modulation of anisotropic hyperfine interactions. The concentration dependence very likely arises from pairwise interactions and cross-relaxation processes. At high temperatures (48–170 K), T 1 is most likely dominated by the Raman process.