Present communication reports the experimental values of the dielectric relaxation time () and dipole moment () of binary mixtures of N-methylformamide (NMF) and dimethylsulphoxid (DMSO) in dilute solution of benzene at wavelength 3.13 cm in the microwave region. The measurements have been made at 293, 303,313 and 323 K, in order to calculate the free energy of activation for dipole orientation process (F). The experimental values of t have been correlated with the calculated value of t obtained using different theories of dielectric relaxation time (  ) for mixtures. It is concluded from this comparative study that both the values are comparable to each other. Thermo dynamical parameters like molar free energy of activation (F), molar enthalpy of activation (H) and molar entropy of activation (S) have been evaluated by considering the relaxation as the rate
process.